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Molecular dynamics simulation and biophysical analysis were employed to reveal the characteristics and the influence of ionic liquids (ILs) on the structural properties of DNA. Both computational and experimental evidence indicate that DNA retains its native B-conformation in ILs. Simulation data show that the hydration shells around the DNA phosphate group were the main criteria for DNA stabilization in this ionic media. Stronger hydration shells reduce the binding ability of ILs' cations to the DNA phosphate group, thus destabilizing the DNA. The simulation results also indicated that the DNA structure maintains its duplex conformation when solvated by ILs at different temperatures up to 373.15 K. The result further suggests that the thermal stability of DNA at high temperatures is related to the solvent thermodynamics, especially entropy and enthalpy of water. All the molecular simulation results were consistent with the experimental findings. The understanding of the properties of IL-DNA could be used as a basis for future development of specific ILs for nucleic acid technology.

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) exhibits a phenomenon known as co-nonsolvency in certain alcohol/water binary mixtures. We have exploited this phenomenon to prepare a series of sterically stabilized PMPC nanolatexes by atom transfer radical polymerization (ATRP) under dispersion polymerization conditions using a near-monodisperse poly(ethylene oxide) (PEO) macroinitiator in a 9:1 isopropanol/water mixture. The as-synthesized nanolatex particles comprised nonsolvated PMPC cores and solvated PEO shells, as determined by 1H NMR spectroscopy. In our preliminary experiments linear core-forming PMPC chains were targeted, but alternatively either ethylene glycol dimethacrylate or bisphenol A dimethacrylate can be used as comonomers (at up to 10 mol % based on MPC) in order to prepare cross-linked PMPC particles that acquire swollen microgel character when dialyzed against pure water. Low levels of cross-linker (e.g., 4 mol %) lead to bimodal microgel size distributions as judged by dynamic light scattering. However, higher levels of cross-linker (e.g., 10 mol %) lead to narrow unimodal microgel size distributions, since all the core-forming PMPC chains become cross-linked. The final nanolatex/microgel dimensions are dictated by the target block compositions and initial MPC concentration used in these ATRP syntheses. A PEO113-b-PMPC50 formulation synthesized at 30 wt % solids produced nanolatex/microgel particles that were 5−6 times larger than those observed for the same block composition prepared at 10 wt % solids. TEM and SEM studies confirm that these new sterically stabilized particles have uniform spherical morphologies. Cross-linked PEO-b-PMPC particles were analyzed by X-ray photoelectron spectroscopy after dialysis against water. The surface coverage of the PEO stabilizer chains was estimated to be 54−61%. Aqueous electrophoresis studies confirmed that the PEO-b-PMPC microgels exhibited almost zero net charge, and the addition of electrolyte had little effect on their dimensions and colloidal stability due to the anti-polyelectrolyte behavior expected for the zwitterionic PMPC chains.

Ruthenium(II) polypyridyl complexes can intercalate DNA with high affinity and prevent cell proliferation; however, the direct impact of ruthenium-based intercalation on cellular DNA replication remains unknown. Here we show the multi-intercalator [Ru(dppz)2(PIP)]2+ (dppz = dipyridophenazine, PIP = 2-(phenyl)imidazo[4,5-f][1,10]phenanthroline) immediately stalls replication fork progression in HeLa human cervical cancer cells. In response to this replication blockade, the DNA damage response (DDR) cell signalling network is activated, with checkpoint kinase 1 (Chk1) activation indicating prolonged replication-associated DNA damage, and cell proliferation is inhibited by G1-S cell-cycle arrest. Co-incubation with a Chk1 inhibitor achieves synergistic apoptosis in cancer cells, with a significant increase in phospho(Ser139) histone H2AX (γ-H2AX) levels and foci indicating increased conversion of stalled replication forks to double-strand breaks (DSBs). Normal human epithelial cells remain unaffected by this concurrent treatment. Furthermore, pre-treatment of HeLa cells with [Ru(dppz)2(PIP)]2+ before external beam ionising radiation results in a supra-additive decrease in cell survival accompanied by increased γ-H2AX expression, indicating the compound functions as a radiosensitizer. Together, these results indicate ruthenium-based intercalation can block replication fork progression and demonstrate how these DNA-binding agents may be combined with DDR inhibitors or ionising radiation to achieve more efficient cancer cell killing.

Abstract:Although metal ion directed self-assembly has been widely used to construct a vast number of macrocycles and cages, it is only recently that the biological properties of these systems have begun to be explored. However, up until now, none of these studies have involved intrinsically photo-excitable self-assembled structures. Herein we report the first metallomacrocycle that functions as an intracellular singlet oxygen sensitizer. Not only does this Ru 2 Re 2 system possess potent photocytotoxicity at light fluences below those used for current medically employed systems, it offers an entirely new paradigm for the construction of sensitizers for photodynamic therapy.

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