Mechanism of action of neothramycin. II. Interaction with DNA.

Abstract

The previous biochemical investigations (MARUYAMA, I. N. et al. J. Antibiotics, 31: 761-768, 1978) suggested that DNA is the chemoreceptor of neothramycin, a new antitumor antibiotic. Therefore, the interaction of the drug with DNA was studied in the current experiments, using UV, circular dichroism and fluorescence spectroscopies, and a [14C]neothramycin binding method. The UV absorption spectrum of neothramycin exhibited bathochromic shift and hypochromic change upon reaction with native calf thymus DNA, indicating a reaction of the antibiotic with DNA. The binding of the drug with native DNA was also demonstrated by circular dichroism. It was further observed that [14C]neothramycin interacted with native DNA. The antibiotic bound to native DNA and poly[dG•dC] more markedly than heat-denatured DNA, poly[dA•dT] and poly[dG] •poly[dC]. Fluorescence of neothramycins A and B was enhanced by native DNA, but not significantly by RNA and heat-denatured DNA. The emission maximum (420 nm) was the same in the presence and absence of DNA. Fluorospectrometric studies revealed that 10, 11-dihydroneothramycins A and B, and their 3-O-butyl derivatives did not bind to DNA; and DNA reacted with 3-O-alkylneothramycin B, but not with 3-O-alkylneothramycin A. The current experiments showed that the reaction rate of neothramycin with native DNA was slower than those of other DNA-binding antibiotics, including anthramycin, tomaymycin, sibiromycin, adriamycin, and actinomycin. The timerequired for neothramycin to saturate DNA was several hours. The results suggested that neothramycin may recognize or interact with a highly specific portion of double helical structure of DNA, and then a covalent bond may be formed between C-11 of the antibiotic and guanine or cytosine base of DNA.