The arrows indicate strand direction from 5′ to 3′. The ability of the three ligands to induce structure in the single stranded h-Tel sequence in aqueous solution in the absence of significant VX 809 concentrations of K+ ions was also investigated. The unfolded h-Tel sequence at 298 K gives a low intensity positive band in the CD spectrum at 265 nm (Figure  4b). However, in the presence of 3.5 molar equivalents of ligand, emergence of the characteristic band at 290 nm was observed, consistent with the ligand-induced formation of

the anti-parallel structures evident in the K+ buffered solution. Thus, under both sets of conditions (with and without stabilising K+ ions), evidence is adduced for ligand selectivity for the anti-parallel quadruplex structure [12, 13]. This analysis was extended to examine the effects of ligand binding on thermal stability by measuring the

unfolding curves at 290 nm of the complexes formed in K+ solution, corresponding to the CD spectra shown in Figure  4a. Monitoring the thermal unfolding transition for h-Tel produces a sigmoidal unfolding curve with a transition mid-point Tm value of 72 ± 3°C (Figure  4c). All three ligands show significant effects in enhancing the stability of the quadruplex by shifting the Tm values to higher temperatures Verteporfin datasheet (∆Tm ~ 15-19°C compared to h-Tel without bound ligands) (Table  1). Biological effects of quinoacridinum salts To ascertain if the compounds 2 and 3 maintained the same biological and molecular features of the previously described 1, we firstly evaluated their effect on cell proliferation in a panel of different Fossariinae histotype tumor cell lines, showing that both compounds maintained an anti-proliferative effect in several human cancer cell lines (Additional file 1). Selectivity for transformed vs normal cells was assessed in the hTERT immortalized BJ human fibroblasts infected or not with the Large T antigen of SV40. Figure  5a and b shows the growth curves of untreated and drug-treated cells, analyzed from day 2 to 8 of culture by using 0.5 μM concentration

of each compound, a dose causing cell death when cells are chronically exposed to the lead compound 1. A time-dependent decrease of cell proliferation was observed in SV40 transformed (BJ-EHLT) cells treated with the ligands reaching the maximum effect at day 6 (for the compounds 1 and 2) or seven (compound 3). AZD8186 clinical trial Interestingly, as already described for 1, the compounds 2 and 3 did not induce inhibition of cell proliferation in normal telomerized fibroblasts, which were unaffected by the treatment (Figure  5a and b). Even if the mechanism(s) of selectivity towards transformed cells were not identified yet, our results indicate that the new-generated agents 2 and 3, similarly to the lead compound, preferentially limit the growth of cancer cells. Figure 5 Anti-proliferative effect on normal and transformed fibroblasts.