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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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Metabolic effects of VCD.Cells were exposed to increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) glucose. (A) Mitochondrial respiration was analyzed by measuring the oxygen consumption rate (OCR; pMoles/min). (B) Glycolytic flux was quantitated by measuring extracellular acidification rate (ECAR; mpH/min).
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pone-0065695-g008: Metabolic effects of VCD.Cells were exposed to increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) glucose. (A) Mitochondrial respiration was analyzed by measuring the oxygen consumption rate (OCR; pMoles/min). (B) Glycolytic flux was quantitated by measuring extracellular acidification rate (ECAR; mpH/min).

Mentions: The bioenergetic effects of VCD were investigated further with the use of the Seahorse analyzer. This piece of equipment is able to quantify mitochondrial respiration by measuring the oxygen consumption rate (OCR); as well, it can quantify glycolytic flux by measuring the extracellular acidification rate (ECAR). Cells were exposed to 100 and 300 nM VCD in the presence and absence of glucose, and OCR and ECAR were measured at 6-minute intervals for up to one hour. The results are summarized in Fig. 8 as follows.


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)

Metabolic effects of VCD.Cells were exposed to increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) glucose. (A) Mitochondrial respiration was analyzed by measuring the oxygen consumption rate (OCR; pMoles/min). (B) Glycolytic flux was quantitated by measuring extracellular acidification rate (ECAR; mpH/min).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0065695-g008: Metabolic effects of VCD.Cells were exposed to increasing concentrations of VCD in the absence (0.0 mM) or presence (25 mM) glucose. (A) Mitochondrial respiration was analyzed by measuring the oxygen consumption rate (OCR; pMoles/min). (B) Glycolytic flux was quantitated by measuring extracellular acidification rate (ECAR; mpH/min).
Mentions: The bioenergetic effects of VCD were investigated further with the use of the Seahorse analyzer. This piece of equipment is able to quantify mitochondrial respiration by measuring the oxygen consumption rate (OCR); as well, it can quantify glycolytic flux by measuring the extracellular acidification rate (ECAR). Cells were exposed to 100 and 300 nM VCD in the presence and absence of glucose, and OCR and ECAR were measured at 6-minute intervals for up to one hour. The results are summarized in Fig. 8 as follows.

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