Figure 1.
Chemical structures of the chelators, Triapine, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), 2-benzoylpyridine 4,4-dimethyl-3-thiosemicarbazone (Bp44mT) and quinoline thiosemicarbazone (QT).
Figure 2.
Synthetic route to yield thiosemicarbazides, a–e.
Figure 3.
Synthetic route to yield the thiosemicarbazide, f.
Figure 4.
Synthetic route to yield the final thiosemicarbazones.
Figure 5.
Chemical structures of the thiosemicarbazone chelators of series 1–6.
Table 1.
Anti-proliferative activity (IC50 values) of the novel thiosemicarbazones in comparison to DFO and Dp44mT in several tumor cell-types and normal human dermal fibroblast (NHDF) cells.
Table 2.
The selectivity of Dp44mT relative to the 5 most potent anti-cancer TSCs, namely 1b, 1d, 2b, 2f and 3c, was examined by calculating their “therapeutic indices”.
Figure 6.
Effect of (A) series 1, (B) series 2, (C) series 3, (D) series 4, (E) series 5 and (F) series 6 chelators, relative to the controls DFO and Dp44mT, on 59Fe mobilization from prelabeled SK-N-MC cells.
Cells were incubated for 3 h/37°C with 59Fe-transferrin (0.75 µM), washed 4 times with ice-cold PBS and then reincubated for 3 h/37°C in the presence or absence of the chelators (25 µM). Release of 59Fe was then assessed using a γ-scintillation counter. Results are mean ±SD (3 experiments).
Figure 7.
Relationship between the cellular iron released (% total) and lipophilicity (logPcalc) of series 1 chelators using SK-N-MC neuroepithelioma cells.
Lines were fitted in using Microsoft Excel 2010 (Microsoft, Redmond, WA).
Figure 8.
Effect of (A) series 1, (B) series 2, (C) series 3, (D) series 4, (E) series 5 and (F) series 6 chelators, relative to the controls DFO and Dp44mT, on 59Fe uptake from 59Fe-transferrin by SK-N-MC cells.
Cells were incubated for 3 h/37°C with 59Fe-transferrin (0.75 µM) in the presence or absence of the chelators (25 µM). At the end of this incubation, cells were washed 4 times with ice-cold PBS. Internalization of 59Fe was assessed by incubation for 30 min/4°C with the protease, Pronase (1 mg/mL). Cellular 59Fe was then assessed using a γ-scintillation counter. Results are mean ±SD (3 experiments).
Figure 9.
Relationship between the internalized iron uptake (% control) and cellular iron released (% total) of series 1–6 using SK-N-MC neuroepithelioma cells.
Lines were fitted in using Microsoft Excel 2010 (Microsoft, Redmond, WA).
Figure 10.
Effect of the iron complexes of (A) series 1, (B) series 2, (C) series 3, (D) series 4, (E) series 5 and (F) series 6 chelators, relative to DFO, Dp44mT and EDTA, on ascorbate oxidation.
Chelators at iron-binding equivalent (IBE) ratios of 0.1, 1, and 3 were incubated in the presence of FeIII (10 µM) and ascorbate (100 µM). The UV-Vis absorbance at 265 nm was recorded after 10 and 40 min, and the difference between the time points was calculated. Results are mean ±SD (3 experiments).