Effect of testosterone and its aliphatic and aromatic dimers on DNA morphology

Conjugation of DNA with testosterone and it aliphatic dimer (alip) and aromatic dimer (arom) was investigated in aqueous solution at pH 7.4. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize steroid-DNA binding and DNA morphology. Spectroscopic analysis showed that testosterone binds DNA via A7, A16, A17, T8, T15 and T18 nucleobases with overall binding constants K_test-DNA=1.8 (±0.4)×10⁴M^-1, K_{test-dimeralip-DNA}=5.7 (±0.7)×10⁴M^-1 and K_{test-dimer-arom-DNA}=7.3 (±0.9)×10⁴M^-1. The binding affinity increases in this order: testosterone dimer-aromatic>testosterone dimer-aliphatic>testosterone. The steroid loading efficacy was 40-50%. Transmission electron microscopy showed major changes in DNA morphology as testosterone-DNA interaction occurred with increase in the diameter of the DNA aggregate, indicating encapsulation of testosterone by DNA. Modeling showed the presence of several nucleobases attached to testosterone with the free binding energy of -4.93Kcal/mol.