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Repositioning of Verrucosidin, a purported inhibitor of chaperone protein GRP78, as an inhibitor of mitochondrial electron transport chain complex I.

Thomas S, Sharma N, Gonzalez R, Pao PW, Hofman FM, Chen TC, Louie SG, Pirrung MC, Schönthal AH - PLoS ONE (2013)

Bottom Line: Rather, VCD blocked mitochondrial energy production via inhibition of complex I of the electron transport chain.Altogether, our study identifies mitochondria as the primary target of VCD.The possibility that other purported GRP78 inhibitors (arctigenin, biguanides, deoxyverrucosidin, efrapeptin, JBIR, piericidin, prunustatin, pyrvinium, rottlerin, valinomycin, versipelostatin) might act in a similar GRP78-independent fashion will be discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Microbiology and Immunology, University of Southern California, Los Angeles, California, United States of America.

ABSTRACT
Verrucosidin (VCD) belongs to a group of fungal metabolites that were identified in screening programs to detect molecules that preferentially kill cancer cells under glucose-deprived conditions. Its mode of action was proposed to involve inhibition of increased GRP78 (glucose regulated protein 78) expression during hypoglycemia. Because GRP78 plays an important role in tumorigenesis, inhibitors such as VCD might harbor cancer therapeutic potential. We therefore sought to characterize VCD's anticancer activity in vitro. Triple-negative breast cancer cell lines MDA-MB-231 and MDA-MB-468 were treated with VCD under different conditions known to trigger increased expression of GRP78, and a variety of cellular processes were analyzed. We show that VCD was highly cytotoxic only under hypoglycemic conditions, but not in the presence of normal glucose levels, and VCD blocked GRP78 expression only when glycolysis was impaired (due to hypoglycemia or the presence of the glycolysis inhibitor 2-deoxyglucose), but not when GRP78 was induced by other means (hypoxia, thapsigargin, tunicamycin). However, VCD's strictly hypoglycemia-specific toxicity was not due to the inhibition of GRP78. Rather, VCD blocked mitochondrial energy production via inhibition of complex I of the electron transport chain. As a result, cellular ATP levels were quickly depleted under hypoglycemic conditions, and common cellular functions, including general protein synthesis, deteriorated and resulted in cell death. Altogether, our study identifies mitochondria as the primary target of VCD. The possibility that other purported GRP78 inhibitors (arctigenin, biguanides, deoxyverrucosidin, efrapeptin, JBIR, piericidin, prunustatin, pyrvinium, rottlerin, valinomycin, versipelostatin) might act in a similar GRP78-independent fashion will be discussed.

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Cell growth inhibition by VCD.MDA-MB-231 and MBA-MD-468 cells were exposed to VCD treatment in cell culture. (A) Cells were treated with increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) of glucose for 48 h and cell viability was determined by MTT assay. Removal of glucose by itself (in the absence of VCD) did not substantially interfere with cell viability during this 48-hour period (not shown). (B) Cells were exposed to VCD in the presence of various concentrations of glucose (as indicated) for 48 h and cell viability was determined by MTT assay. (C) Cells were exposed to increasing concentrations of VCD in the presence of 25 mM (left panel) or 0.8 mM (right panel) glucose for 48 h; thereafter, VCD was removed and culture conditions were continued in 25 mM glucose for all cells. Long-term cell survival was determined by counting the number of emerging colonies two weeks later. In all cases, survival of untreated control cells was set at 100%. All values are n≥3 (±s.d.).
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pone-0065695-g001: Cell growth inhibition by VCD.MDA-MB-231 and MBA-MD-468 cells were exposed to VCD treatment in cell culture. (A) Cells were treated with increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) of glucose for 48 h and cell viability was determined by MTT assay. Removal of glucose by itself (in the absence of VCD) did not substantially interfere with cell viability during this 48-hour period (not shown). (B) Cells were exposed to VCD in the presence of various concentrations of glucose (as indicated) for 48 h and cell viability was determined by MTT assay. (C) Cells were exposed to increasing concentrations of VCD in the presence of 25 mM (left panel) or 0.8 mM (right panel) glucose for 48 h; thereafter, VCD was removed and culture conditions were continued in 25 mM glucose for all cells. Long-term cell survival was determined by counting the number of emerging colonies two weeks later. In all cases, survival of untreated control cells was set at 100%. All values are n≥3 (±s.d.).

Mentions: Two triple-negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468, were exposed to increasing concentrations of VCD in the presence or absence of glucose, and cell survival was investigated. As determined by MTT assay, VCD was highly cytotoxic in the absence of glucose, with an IC50 of about 120 nM in both cell lines (Fig. 1A). In stark contrast, VCD concentrations of up to 100,000 nM were only weakly effective and killed less than 50% of the cells under normal (25 mM glucose) culture conditions. Complete absence of glucose was not necessary for VCD to unfold its potent cytotoxicity, as this compound very effectively reduced cellular survival in the presence of 0.25 and 2.5 mM glucose as well (Fig. 1B).


Repositioning of Verrucosidin, a purported inhibitor of chaperone protein GRP78, as an inhibitor of mitochondrial electron transport chain complex I.

Thomas S, Sharma N, Gonzalez R, Pao PW, Hofman FM, Chen TC, Louie SG, Pirrung MC, Schönthal AH - PLoS ONE (2013)

Cell growth inhibition by VCD.MDA-MB-231 and MBA-MD-468 cells were exposed to VCD treatment in cell culture. (A) Cells were treated with increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) of glucose for 48 h and cell viability was determined by MTT assay. Removal of glucose by itself (in the absence of VCD) did not substantially interfere with cell viability during this 48-hour period (not shown). (B) Cells were exposed to VCD in the presence of various concentrations of glucose (as indicated) for 48 h and cell viability was determined by MTT assay. (C) Cells were exposed to increasing concentrations of VCD in the presence of 25 mM (left panel) or 0.8 mM (right panel) glucose for 48 h; thereafter, VCD was removed and culture conditions were continued in 25 mM glucose for all cells. Long-term cell survival was determined by counting the number of emerging colonies two weeks later. In all cases, survival of untreated control cells was set at 100%. All values are n≥3 (±s.d.).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3675020&req=5

pone-0065695-g001: Cell growth inhibition by VCD.MDA-MB-231 and MBA-MD-468 cells were exposed to VCD treatment in cell culture. (A) Cells were treated with increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) of glucose for 48 h and cell viability was determined by MTT assay. Removal of glucose by itself (in the absence of VCD) did not substantially interfere with cell viability during this 48-hour period (not shown). (B) Cells were exposed to VCD in the presence of various concentrations of glucose (as indicated) for 48 h and cell viability was determined by MTT assay. (C) Cells were exposed to increasing concentrations of VCD in the presence of 25 mM (left panel) or 0.8 mM (right panel) glucose for 48 h; thereafter, VCD was removed and culture conditions were continued in 25 mM glucose for all cells. Long-term cell survival was determined by counting the number of emerging colonies two weeks later. In all cases, survival of untreated control cells was set at 100%. All values are n≥3 (±s.d.).
Mentions: Two triple-negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468, were exposed to increasing concentrations of VCD in the presence or absence of glucose, and cell survival was investigated. As determined by MTT assay, VCD was highly cytotoxic in the absence of glucose, with an IC50 of about 120 nM in both cell lines (Fig. 1A). In stark contrast, VCD concentrations of up to 100,000 nM were only weakly effective and killed less than 50% of the cells under normal (25 mM glucose) culture conditions. Complete absence of glucose was not necessary for VCD to unfold its potent cytotoxicity, as this compound very effectively reduced cellular survival in the presence of 0.25 and 2.5 mM glucose as well (Fig. 1B).

Bottom Line: Rather, VCD blocked mitochondrial energy production via inhibition of complex I of the electron transport chain.Altogether, our study identifies mitochondria as the primary target of VCD.The possibility that other purported GRP78 inhibitors (arctigenin, biguanides, deoxyverrucosidin, efrapeptin, JBIR, piericidin, prunustatin, pyrvinium, rottlerin, valinomycin, versipelostatin) might act in a similar GRP78-independent fashion will be discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Microbiology and Immunology, University of Southern California, Los Angeles, California, United States of America.

ABSTRACT
Verrucosidin (VCD) belongs to a group of fungal metabolites that were identified in screening programs to detect molecules that preferentially kill cancer cells under glucose-deprived conditions. Its mode of action was proposed to involve inhibition of increased GRP78 (glucose regulated protein 78) expression during hypoglycemia. Because GRP78 plays an important role in tumorigenesis, inhibitors such as VCD might harbor cancer therapeutic potential. We therefore sought to characterize VCD's anticancer activity in vitro. Triple-negative breast cancer cell lines MDA-MB-231 and MDA-MB-468 were treated with VCD under different conditions known to trigger increased expression of GRP78, and a variety of cellular processes were analyzed. We show that VCD was highly cytotoxic only under hypoglycemic conditions, but not in the presence of normal glucose levels, and VCD blocked GRP78 expression only when glycolysis was impaired (due to hypoglycemia or the presence of the glycolysis inhibitor 2-deoxyglucose), but not when GRP78 was induced by other means (hypoxia, thapsigargin, tunicamycin). However, VCD's strictly hypoglycemia-specific toxicity was not due to the inhibition of GRP78. Rather, VCD blocked mitochondrial energy production via inhibition of complex I of the electron transport chain. As a result, cellular ATP levels were quickly depleted under hypoglycemic conditions, and common cellular functions, including general protein synthesis, deteriorated and resulted in cell death. Altogether, our study identifies mitochondria as the primary target of VCD. The possibility that other purported GRP78 inhibitors (arctigenin, biguanides, deoxyverrucosidin, efrapeptin, JBIR, piericidin, prunustatin, pyrvinium, rottlerin, valinomycin, versipelostatin) might act in a similar GRP78-independent fashion will be discussed.

Show MeSH
Related in: MedlinePlus