Piperazinyl fragment improves anticancer activity of Triapine

<div><p>A new class of TSCs containing piperazine (piperazinylogs) of Triapine, was designed to fulfill the di-substitution pattern at the TSCs N4 position, which is a crucial prerequisite for the high activity of the previously obtained TSC compounds–DpC and Dp44mT. We tested the important physicochemical characteristics of the novel compounds L¹-L¹². The studied ligands are neutral at physiological pH, which allows them to permeate cell membranes and bind cellular Fe pools more readily than less lipid-soluble ligands, e.g. DFO. The selectivity and anti-cancer activity of the novel TSCs were examined in a variety of cancer cell types. In general, the novel compounds demonstrated the greatest promise as anti-cancer agents with both a potent and selective anti-proliferative activity. We investigated the mechanism of action more deeply, and revealed that studied compounds inhibit the cell cycle (G1/S phase). Additionally we detected apoptosis, which is dependent on cell line’s specific genetic profile. Accordingly, structure-activity relationship studies suggest that the combination of the piperazine ring with Triapine allows potent and selective anticancer chelators that warrant further <i>in vivo</i> examination to be identified. Significantly, this study proved the importance of the di-substitution pattern of the amine N4 function.</p></div

Design strategy for novel TSCs (L¹-L¹²).

<p>All designed ligands are based on the Triapine skeleton, which is present in the active analogs Dp44mT, DpC and 1b, 1d that have been described as highly active analogs [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188767#pone.0188767.ref021" target="_blank">21</a>].</p

Piperazinyl fragment improves anticancer activity of Triapine - Fig 3

<p>(a) Absorption spectrophotometric titration vs. pH of the free L² ligand; (b) electronic spectra of the protonated species of L²; (c) concentration distribution curves for the L² species. (I = 0.1 M (KCl) in 80% (w/w) MeOH/H₂O; T = 25.0°C; [L²] = 5x10^-5M; pH 1.6–11.02).</p

Protonation constants (log<i>β</i> ^H) of the L¹-L¹² ligands in the MeOH/H₂O mixed solution^a.

<p>Protonation constants (log<i>β</i> ^H) of the L¹-L¹² ligands in the MeOH/H₂O mixed solution<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188767#t001fn001" target="_blank">^a</a>.</p

Electronic absorption spectra of the Cu(II) and Fe(III)-L²; L⁴; L⁸ system recorded at various metal to ligand ratios.

<p>I = 0.1 M (KCl) in 80% (w/w) MeOH/H₂O; T = 25.0°C; [L] = 5x10^-5M.</p

Anti-proliferative activity (IC₅₀ values) of the novel Triapine analogs compared to Triapine in several tumor cell-types and normal human dermal fibroblast (NHDF) cells.

<p>Individual IC50 values IC50 < 1μM, IC50 1–10 μM, IC50 > 10 μM are coded by red, yellow and grey, respectively.</p

Evaluation of the induction of apoptosis in the HCT116 p53^+/+, U-251 and MCF-7 cells 48 h after treatment with L⁹.

<p>The histograms show the percentage of early and late apoptosis for one of three independent experiments (<b>A</b>). The table shows the mean ± SD percentage of live, early and late apoptotic cells from three independent experiments (<b>B</b>). Data were analyzed using one-way ANOVA with Bonferroni’s post-hoc test: *p<0.05, **p<0.01, ***p<0.001 compared to the control (<b>C</b>).</p