Multiple mechanisms for cytotoxicity induced by copper(II) complexes of 2‐acetylpyrazine‐N‐substituted thiosemicarbazones

Abstract

The purpose of this study was to evaluate the mechanism by which 2-acetylpyrazine-4 N-substituted thiosemicarbazone copper II complexes mediate their cytotoxicity. These compounds were shown to be cytotoxic to a variety of human and rodent tumors in cell culture and are potent cytocidal agents as determined by dilute agar colony assays. They demonstrated the ability to inhibit several enzymes in vitro including DNA topoisomerase II activity. The data presented suggest that cytotoxicity may be mediated by the cumulative effect of several enzymes being inhibited by the agents. Copyright #

Role of Metalation in the Topoisomerase IIα Inhibition and Antiproliferation Activity of a Series of α-Heterocyclic-N4-Substituted Thiosemicarbazones and Their Cu(II) Complexes

“…Experiments with the Cu(TSC)Cl complexes revealed that all of the complexes are active antiproliferative agents, with GI 50 of <1 to 6 μM with SK-BR-3 cells and 2 to 12 μM with MCF-7 cells (Chart ). These values are in general agreement with those previously reported for Cu(TSC)Cl complexes and human cancer cells. − , Again, few structure−activity relationships are evident. However, two trends suggest that Topo-IIα inhibition may play a role in the antiproliferative effects of these complexes.…”

“…Notably, the IC 50 values for the Cu(TSC)Cl complexes are comparable to those of the well-characterized Topo-IIR inhibitor doxorubicin (1-5 μM) and lie well below those of the Topo-IIR inhibitors merbarone (40-50 μM) and etoposide (50-90 μM). [24][25][26][27] Further, these values generally agree with the in vitro IC 50 and the in vivo concentrations at which Topo-IIR inhibition was observed in the studies of Miller et al [12][13][14] Similarly, the in vitro Topo-IIR IC 50 values for the TSCs generally conform to those found for R-heterocyclic TSCs in Miller's study of acetylpyridyl-N 4 substituted thiosemicarbazones and the recently published work of Huang and co-workers. 13,17 Further still, a recent study with di-2pyridylketone-4,4-dimethylthiosemicarbazone (Dp44mT) found evidence of in vivo Topo-IIR inhibition at very low concentrations (<1 μM); this finding, however, is not inconsistent with the data described herein because of the significant structural difference of Dp44mT compared to the compounds at hand and because of the in vivo nature of the experiments.…”

“…Further, the Cu I/II redox cycling of these complexes, like their Fe II cousins, plays a significant role in their biological activity . Importantly, this work and that of others strongly support the hypothesis that it is the copper complexes rather than any dissociated ligands or cellular metabolites that are responsible for the biological effects in vitro and in vivo. − …”

Role of Metalation in the Topoisomerase IIα Inhibition and Antiproliferation Activity of a Series of α-Heterocyclic-N4-Substituted Thiosemicarbazones and Their Cu(II) Complexes

“…Experiments with the Cu(TSC)Cl complexes revealed that all of the complexes are active antiproliferative agents, with GI 50 of <1 to 6 μM with SK-BR-3 cells and 2 to 12 μM with MCF-7 cells (Chart ). These values are in general agreement with those previously reported for Cu(TSC)Cl complexes and human cancer cells. − , Again, few structure−activity relationships are evident. However, two trends suggest that Topo-IIα inhibition may play a role in the antiproliferative effects of these complexes.…”

“…Notably, the IC 50 values for the Cu(TSC)Cl complexes are comparable to those of the well-characterized Topo-IIR inhibitor doxorubicin (1-5 μM) and lie well below those of the Topo-IIR inhibitors merbarone (40-50 μM) and etoposide (50-90 μM). [24][25][26][27] Further, these values generally agree with the in vitro IC 50 and the in vivo concentrations at which Topo-IIR inhibition was observed in the studies of Miller et al [12][13][14] Similarly, the in vitro Topo-IIR IC 50 values for the TSCs generally conform to those found for R-heterocyclic TSCs in Miller's study of acetylpyridyl-N 4 substituted thiosemicarbazones and the recently published work of Huang and co-workers. 13,17 Further still, a recent study with di-2pyridylketone-4,4-dimethylthiosemicarbazone (Dp44mT) found evidence of in vivo Topo-IIR inhibition at very low concentrations (<1 μM); this finding, however, is not inconsistent with the data described herein because of the significant structural difference of Dp44mT compared to the compounds at hand and because of the in vivo nature of the experiments.…”

“…Further, the Cu I/II redox cycling of these complexes, like their Fe II cousins, plays a significant role in their biological activity . Importantly, this work and that of others strongly support the hypothesis that it is the copper complexes rather than any dissociated ligands or cellular metabolites that are responsible for the biological effects in vitro and in vivo. − …”

Advances in Copper Complexes as Anticancer Agents

“…Further, the Cu­(I)/Cu­(II) redox cycling of these complexes, like their Fe­(II/III) analogs, played a significant role in their biological activity . This work and others strongly supported the hypothesis that the copper complexes rather than any dissociated ligands or cellular metabolites were responsible for the biological effects in vitro and in vivo. − Interestingly, the study of the Cu­(II) coordination chemistry of these compounds revealed that both 1:1 and 1:2 Cu/ligand complexes could be isolated and that the 1:2 complexes dissociated to give significant amounts of the 1:1 species. The higher biological activity of the 1:1 complexes suggested that they may be the active species in cells, while the 1:2 complexes could be precursors to the 1:1 complex formed by partial dissociation.…”

The Cytotoxicity of Symmetrical and Unsymmetrical Bis(thiosemicarbazones) and Their Metal Complexes in Murine and Human Tumor Cells

“…In fact the resulting ED 50 values for the nickel bis(thiosemicarbazones) were essentially the same as the previously reported nickel thiosemicarbazones [3] . The cytotoxic values of the copper(II) complexes, 10-29, were very similar to the uncomplexed bis(thiosemicarbazones), 1-3, as well as the copper(II) complexes of heterocyclic thiosemicarbazones [4][5][6] in blocking the growth of suspended tumor cell growth.…”

Role of Metalation in the Topoisomerase IIα Inhibition and Antiproliferation Activity of a Series of α-Heterocyclic-N4-Substituted Thiosemicarbazones and Their Cu(II) Complexes

“…Experiments with the Cu(TSC)Cl complexes revealed that all of the complexes are active antiproliferative agents, with GI 50 of <1 to 6 μM with SK-BR-3 cells and 2 to 12 μM with MCF-7 cells (Chart ). These values are in general agreement with those previously reported for Cu(TSC)Cl complexes and human cancer cells. − , Again, few structure−activity relationships are evident. However, two trends suggest that Topo-IIα inhibition may play a role in the antiproliferative effects of these complexes.…”

“…Notably, the IC 50 values for the Cu(TSC)Cl complexes are comparable to those of the well-characterized Topo-IIR inhibitor doxorubicin (1-5 μM) and lie well below those of the Topo-IIR inhibitors merbarone (40-50 μM) and etoposide (50-90 μM). [24][25][26][27] Further, these values generally agree with the in vitro IC 50 and the in vivo concentrations at which Topo-IIR inhibition was observed in the studies of Miller et al [12][13][14] Similarly, the in vitro Topo-IIR IC 50 values for the TSCs generally conform to those found for R-heterocyclic TSCs in Miller's study of acetylpyridyl-N 4 substituted thiosemicarbazones and the recently published work of Huang and co-workers. 13,17 Further still, a recent study with di-2pyridylketone-4,4-dimethylthiosemicarbazone (Dp44mT) found evidence of in vivo Topo-IIR inhibition at very low concentrations (<1 μM); this finding, however, is not inconsistent with the data described herein because of the significant structural difference of Dp44mT compared to the compounds at hand and because of the in vivo nature of the experiments.…”

“…Further, the Cu I/II redox cycling of these complexes, like their Fe II cousins, plays a significant role in their biological activity . Importantly, this work and that of others strongly support the hypothesis that it is the copper complexes rather than any dissociated ligands or cellular metabolites that are responsible for the biological effects in vitro and in vivo. − …”

Advances in Copper Complexes as Anticancer Agents

“…Further, the Cu­(I)/Cu­(II) redox cycling of these complexes, like their Fe­(II/III) analogs, played a significant role in their biological activity . This work and others strongly supported the hypothesis that the copper complexes rather than any dissociated ligands or cellular metabolites were responsible for the biological effects in vitro and in vivo. − Interestingly, the study of the Cu­(II) coordination chemistry of these compounds revealed that both 1:1 and 1:2 Cu/ligand complexes could be isolated and that the 1:2 complexes dissociated to give significant amounts of the 1:1 species. The higher biological activity of the 1:1 complexes suggested that they may be the active species in cells, while the 1:2 complexes could be precursors to the 1:1 complex formed by partial dissociation.…”

The Cytotoxicity of Symmetrical and Unsymmetrical Bis(thiosemicarbazones) and Their Metal Complexes in Murine and Human Tumor Cells

“…In fact the resulting ED 50 values for the nickel bis(thiosemicarbazones) were essentially the same as the previously reported nickel thiosemicarbazones [3] . The cytotoxic values of the copper(II) complexes, 10-29, were very similar to the uncomplexed bis(thiosemicarbazones), 1-3, as well as the copper(II) complexes of heterocyclic thiosemicarbazones [4][5][6] in blocking the growth of suspended tumor cell growth.…”

Role of Metalation in the Topoisomerase IIα Inhibition and Antiproliferation Activity of a Series of α-Heterocyclic-N4-Substituted Thiosemicarbazones and Their Cu(II) Complexes

“…Experiments with the Cu(TSC)Cl complexes revealed that all of the complexes are active antiproliferative agents, with GI 50 of <1 to 6 μM with SK-BR-3 cells and 2 to 12 μM with MCF-7 cells (Chart ). These values are in general agreement with those previously reported for Cu(TSC)Cl complexes and human cancer cells. − , Again, few structure−activity relationships are evident. However, two trends suggest that Topo-IIα inhibition may play a role in the antiproliferative effects of these complexes.…”

“…Notably, the IC 50 values for the Cu(TSC)Cl complexes are comparable to those of the well-characterized Topo-IIR inhibitor doxorubicin (1-5 μM) and lie well below those of the Topo-IIR inhibitors merbarone (40-50 μM) and etoposide (50-90 μM). [24][25][26][27] Further, these values generally agree with the in vitro IC 50 and the in vivo concentrations at which Topo-IIR inhibition was observed in the studies of Miller et al [12][13][14] Similarly, the in vitro Topo-IIR IC 50 values for the TSCs generally conform to those found for R-heterocyclic TSCs in Miller's study of acetylpyridyl-N 4 substituted thiosemicarbazones and the recently published work of Huang and co-workers. 13,17 Further still, a recent study with di-2pyridylketone-4,4-dimethylthiosemicarbazone (Dp44mT) found evidence of in vivo Topo-IIR inhibition at very low concentrations (<1 μM); this finding, however, is not inconsistent with the data described herein because of the significant structural difference of Dp44mT compared to the compounds at hand and because of the in vivo nature of the experiments.…”

“…Further, the Cu I/II redox cycling of these complexes, like their Fe II cousins, plays a significant role in their biological activity . Importantly, this work and that of others strongly support the hypothesis that it is the copper complexes rather than any dissociated ligands or cellular metabolites that are responsible for the biological effects in vitro and in vivo. − …”

Advances in Copper Complexes as Anticancer Agents

“…Further, the Cu­(I)/Cu­(II) redox cycling of these complexes, like their Fe­(II/III) analogs, played a significant role in their biological activity . This work and others strongly supported the hypothesis that the copper complexes rather than any dissociated ligands or cellular metabolites were responsible for the biological effects in vitro and in vivo. − Interestingly, the study of the Cu­(II) coordination chemistry of these compounds revealed that both 1:1 and 1:2 Cu/ligand complexes could be isolated and that the 1:2 complexes dissociated to give significant amounts of the 1:1 species. The higher biological activity of the 1:1 complexes suggested that they may be the active species in cells, while the 1:2 complexes could be precursors to the 1:1 complex formed by partial dissociation.…”

The Cytotoxicity of Symmetrical and Unsymmetrical Bis(thiosemicarbazones) and Their Metal Complexes in Murine and Human Tumor Cells

“…In fact the resulting ED 50 values for the nickel bis(thiosemicarbazones) were essentially the same as the previously reported nickel thiosemicarbazones [3] . The cytotoxic values of the copper(II) complexes, 10-29, were very similar to the uncomplexed bis(thiosemicarbazones), 1-3, as well as the copper(II) complexes of heterocyclic thiosemicarbazones [4][5][6] in blocking the growth of suspended tumor cell growth.…”