PT-ACRAMTU, A Platinum–Acridine Anticancer Agent, Lengthens and Aggregates, but does not Stiffen or Soften DNA
We used atomic force microscopy (AFM) to study the dose-dependent change in conformational and mechanical properties of DNA treated with PT-ACRAMTU ([PtCl(en)(ACRAMTU-S)](NO3)2, (en = ethane-1,2-diamine, ACRAMTU = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea. PT-ACRAMTU is the parent drug of a family of non-classical platinum-based agents that show potent activity in non-small cell lung cancer in vitro and in vivo. Its acridine moiety intercalates between DNA bases, while the platinum group forms mono-adducts with DNA bases. AFM images show that PT-ACRAMTU causes some DNA looping and aggregation at drug-to-base pair ratio (r b) of 0.1 and higher. Very significant lengthening of the DNA was observed with increasing doses of PT-ACRAMTU, and reached saturation at an r b of 0.15. At r b of 0.1, lengthening was 0.6 nm per drug molecule, which is more than one fully stretched base pair stack can accommodate, indicating that ACRAMTU also disturbs the stacking of neighboring base pair stacks. Analysis of the AFM images based on the worm-like chain (WLC) model showed that PT-ACRAMTU did not change the flexibility of (non-aggregated) DNA, despite the extreme lengthening. The persistence length of untreated DNA and DNA treated with PT-ACRAMTU was in the range of 49–65 nm. Potential consequences of the perturbations caused by this agent for the recognition and processing of the DNA adducts it forms are discussed.
KeywordsAcramtu Cancer drug DNA lengthening Persistence length
We thank Lu Rao for technical support with DNA-drug incubations. This work was supported by the National Science Foundation [CMMI-0646627, to M.G.], the North Carolina Biotechnology Center [2011-MRG-1115, to M.G.], and the National Institutes of Health [CA101880, to U.B.].
- 1.Eastman, A. (1990). Activation of programmed cell death by anticancer agents—cisplatin as a model system. Cancer Cells-A Monthly Review, 2, 275–280.Google Scholar
- 9.Hess, S. M., Mounce, A. M., Sequeira, R. C., Augustus, T. M., Ackley, M. C., & Bierbach, U. (2005). Platinum-acridinylthiourea conjugates show cell line-specific cytotoxic enhancement in H460 lung carcinoma cells compared to cisplatin. Cancer Chemotherapy and Pharmacology, 56, 337–343.PubMedCrossRefGoogle Scholar
- 11.Baruah, H., Rector, C. L., Monnier, S. M., & Bierbach, U. (2002). Mechanism of action of non-cisplatin type DNA-targeted platinum anticancer agents: DNA interactions of novel acridinylthioureas and their platinum conjugates (vol 64, pg 191, 2002). Biochemical Pharmacology, 64, 751.CrossRefGoogle Scholar
- 14.Kostrhunova, H., Malina, J., Pickard, A. J., Stepankova, J., Vojtiskova, M., Kasparkova, J., et al. (2011). Replacement of a thiourea with an amidine group in a monofunctional platinum-acridine antitumor agent. Effect on DNA interactions, DNA adduct recognition and repair. Molecular Pharmaceutics, 8, 1941–1954.PubMedCrossRefGoogle Scholar
- 23.Barry, C. G., Baruah, H., & Bierbach, U. (2003). Unprecedented monofunctional metalation of adenine nucleobase in guanine- and thymine-containing dinucleotide sequences by a cytotoxic platinum-acridine hybrid agent. Journal of the American Chemical Society, 125, 9629–9637.PubMedCrossRefGoogle Scholar
- 27.Landau, L. D., Lifshitz, E. M. (1980). Statistical physics Part 1. 3rd edn.Google Scholar
- 28.Kratky, O., Porod, G. (1949). Röntgenuntersuchungaufgelöster Fadenmoleküle. Recueil 68:1106–1122.Google Scholar
- 31.Flory, P. J. (1969). Statistical mechanics of chain molecules. New York: Interscience Publishers.Google Scholar
- 47.Shui, X. Q., Peek, M. E., Lipscomb, L. A., Gao, Q., Ogata, C., Roques, B. P., et al. (2000). Effects of cationic charge on three-dimensional structures of intercalative complexes: Structure of a bis-intercalated DNA complex solved by MAD phasing. Current Medicinal Chemistry, 7, 59–71.PubMedCrossRefGoogle Scholar