Background

Chemotherapeutic agents (anti-cancer drugs) are small cytostatic or cytotoxic molecules that often bind to double-stranded DNA (dsDNA) resulting in modifications of their structural and nanomechanical properties and thus interfering with the cell proliferation process.

Methods

We investigated the anthraquinone compound mitoxantrone that is used for treating certain cancer types like leukemia and lymphoma with magnetic tweezers as a single molecule nanosensor. In order to study the association of mitoxantrone with dsDNA, we conducted force-extension and mechanical overwinding experiments with a sensitivity of 10−14 N.

Results

Using this method, we were able to estimate an equilibrium constant of association Ka ≈ 1 × 105 M−1 as well as a binding site size of n ≈ 2.5 base pairs for mitoxantrone. An unwinding angle of mitoxantrone-intercalation of ϑ ≈ 16° was determined.

Conclusion

Moreover, we observed a complex concentration-dependent bimodal binding behavior, where mitoxantrone associates to dsDNA as an intercalator and groove binder simultaneously at low concentrations and as a mere intercalator at high concentrations.