Deciphering molecular aspects of interaction between anticancer drug mitoxantrone and tRNA

Mitoxantrone (1,4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)amino]ethyl]amino]-9,10-anthracenedione) is a synthetically designed antineoplastic agent and structurally similar to classical anthracyclines. It is widely used as a potent chemotherapeutic component against various kinds of cancer and possesses lesser cardio-toxic effects with respect to naturally occurring anthracyclines. In the present study, we have investigated the binding features of mitoxantrone-tRNA complexation at physiological pH using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, circular dichroism (CD) spectroscopy, isothermal titration calorimetry, and UV-visible absorption spectroscopic techniques. FTIR analysis reveals that mitoxantrone interacts mainly with heterocyclic base residues of tRNA along with slight external binding with phosphate-sugar backbone. In particular, mitoxantrone binds at uracil (C=O) and adenine (C=N) sites of biomolecule (tRNA). CD spectroscopic results suggest that there is no major conformational transition in native A-form of tRNA upon mitoxantrone-tRNA adductation except an intensification in the secondary structure of tRNA is evident. The association constant calculated for mitoxantrone-tRNA association is found to be 1.27 × 10⁵ M^-1 indicating moderate to strong binding affinity of drug with tRNA. Thermodynamically, mitoxantrone-tRNA interaction is an enthalpy-driven exothermic reaction. Investigation into drug-tRNA interaction can play an essential role in the rational development of RNA targeting chemotherapeutic agents, which also delineate the structural-functional relationship between drug and its target at molecular level.