Calf Thymus DNA Exposed to Quinacrine at Physiological Temperatures and pH Acquires Immunogenicity: A Threat for Long Term Quinacrine Therapy

Abstract

Quinacrine is an Acridine derivative with two potentially reactive groups; a diamino butyl side chain and an Acridine ring both capable of interacting with DNA but in different ways. This is an antimalarial drug approved by FDA for long term clinical trials and for the treatment of other diseases as well. The study evaluates the physicochemical interactions of quinacrine with DNA (calf thymus DNA) through characterizations of quinacrine DNA adduct (Q-DNA) by various techniques. It was observed that quinacrine induces stability in the structure of DNA, as the onset of melting was found to be increased by 6 °C in the melting temperature profile of Q-DNA supported by other data obtained during study, deviation from the native structure of DNA was analyzed by FTIR that showed specific shifts in the region of 1707-1400 cm^-1.The study also probed the antigenicity of Q-DNA compared to its non antigenic native counterpart (N-DNA), by using both as antigens in female New Zealand White rabbits. Q-DNA was found to be antigenic with antibody titer > 1:6400. IgG was isolated and characterized to check for binding specificity. These antibodies were found to be promiscuous capable of cross reacting with other cellular molecules. Analysis of the data obtained suggested that intracellular accumulation of quinacrine and its ability to cross nucleus may allow the drug to interact with DNA. This may bring about significant structural perturbations in the macromolecule triggering an immunogenic response at the site where anti Q-DNA antibody and Q-DNA complex accumulates.

Keywords: Antigenicity; DNA; ELISA; Quinacrine.

Fig. 1

Non covalent bimodal quinacrine interaction with calf thymus DNA through planar aromatic acridine ring and aliphatic diaminobutyl side chain

Fig. 2

Thermal denaturation profile of N-DNA (-) and Q-DNA (-). The above result is an average of 3 independent experiments

Fig. 3

FTIR spectroscopy of N-DNA (-) and Q-DNA (-)

Fig. 4

Direct binding ELISA of (A) N-DNA and (B) Q-DNA with pre-immune (-●-) and immune (-■-) sera. The result represents an average of data obtained in duplicates

Fig. 5

Inhibition ELISA of (A) N-DNA, (B) Q-DNA with pre-immune (-●-) and immune (-■-) sera and (C) represents inhibition ELISA of N-DNA (-●-) and Q-DNA (-■-) by anti-Q-DNA IgG (Isolated from immune sera). Microtitre plates were coated with Q-DNA (2.5 µg/ml). The result represents an average of data obtained in duplicates