Disruption of mitochondrial function as mechanism for anti-cancer activity of a novel mitochondriotropic menadione derivative.

Menadione, also known as vitamin K3, is a 2-methyl-1,4 naphthoquinone with a potent cytotoxic activity mainly resulting from its quinone redox-cycling with production of reactive oxygen species (ROS). Although increased ROS generation is considered a relevant mechanism in cancer cell death, it may not be sufficiently effective to kill cancer cells due to phenotypic adaptations. Therefore, combining ROS-generating agents with other molecules targeting important cancer cell phenotypes can be an effective therapeutic strategy. As mitochondrial dysfunction has been implicated in many human diseases, including cancer, we describe here the discovery of a mitochondrial-directed agent (MitoK3), which was developed by conjugating a TPP cation to the C3 position of the menadione's naphthoquinone ring, increasing its selective accumulation in mitochondria, as well as led to alterations of its redox properties and consequent biological outcome. MitoK3 disturbed the mitochondrial bioenergetic apparatus, with subsequent loss of mitochondrial ATP production. The combinatory strategy of MitoK3 with anticancer agent doxorubicin (DOX) resulted in a degree of cytotoxicity higher than those of the individual molecules, as the combination triggered tumour apoptotic cell death evident by caspase 3/9 activities, probably through mitochondrial destabilization or by interference with mitochondrial redox processes. The results of this investigation support the importance of drug discovery process in developing molecules that can be use as adjuvant therapy in patients with specific cancer subtypes.

Berberine as a promising safe anti-cancer agent - is there a role for mitochondria?

Metabolic regulation is largely dependent on mitochondria, which play an important role in energy homeostasis. Imbalance between energy intake and expenditure leads to mitochondrial dysfunction, characterized by a reduced ratio of energy production (ATP production) to respiration. Due to the role of mitochondrial factors/events in several apoptotic pathways, the possibility of targeting that organelle in the tumor cell, leading to its elimination is very attractive, although the safety issue is problematic. Berberine, a benzyl-tetra isoquinoline alkaloid extracted from plants of the Berberidaceae family, has been extensively used for many centuries, especially in the traditional Chinese and Native American medicine. Several evidences suggest that berberine possesses several therapeutic uses, including anti-tumoral activity. The present review supplies evidence that berberine is a safe anti-cancer agent, exerting several effects on mitochondria, including inhibition of mitochondrial Complex I and interaction with the adenine nucleotide translocator which can explain several of the described effects on tumor cells.

Mitochondrially targeted effects of berberine [Natural Yellow 18, 5,6-dihydro-9,10-dimethoxybenzo(g)-1,3-benzodioxolo(5,6-a) quinolizinium] on K1735-M2 mouse melanoma cells: comparison with direct effects on isolated mitochondrial fractions.

Berberine [Natural Yellow 18, 5,6-dihydro-9,10-dimethoxybenzo(g)-1,3-benzodioxolo(5,6-a)quinolizinium] is an alkaloid present in plant extracts and has a history of use in traditional Chinese and Native American medicine. Because of its ability to arrest the cell cycle and cause apoptosis of several malignant cell lines, it has received attention as a potential anticancer therapeutic agent. Previous studies suggest that mitochondria may be an important target of berberine, but relatively little is known about the extent or molecular mechanisms of berberine-mitochondrial interactions. The objective of the present work was to investigate the interaction of berberine with mitochondria, both in situ and in isolated mitochondrial fractions. The data show that berberine is selectively accumulated by mitochondria, which is accompanied by arrest of cell proliferation, mitochondrial fragmentation and depolarization, oxidative stress, and a decrease in ATP levels. Electron microscopy of berberine-treated cells shows a reduction in mitochondria-like structures, accompanied by a decrease in mitochondrial DNA copy number. Isolated mitochondrial fractions treated with berberine had slower mitochondrial respiration, especially when complex I substrates were used, and increased complex I-dependent oxidative stress. It is also demonstrated for the first time that berberine stimulates the mitochondrial permeability transition. Direct effects on ATPase activity were not detected. The present work demonstrates a number of previously unknown alterations of mitochondrial physiology induced by berberine, a potential chemotherapeutic agent, although it also suggests that high doses of berberine should not be used without a proper toxicology assessment.

Inhibition of mitochondrial bioenergetics by carbaryl is only evident for higher concentrations -- Relevance for carbaryl toxicity mechanisms.

Although pesticides have been useful in agriculture pest control, there is a considerable risk for human health and damage to ecosystems. Carbaryl is a carbamate often taken as a safe insecticide, although data on metabolic activities is still scarce, viz. mitochondrial toxicity. Therefore, it is the goal of this work to assay the compound on isolated mitochondria, a biochemical model already used with other pesticides. Mitochondria isolated from the livers of Wistar rats were assayed for bioenergetic parameters, namely mitochondrial respiration, membrane potential, membrane integrity and enzyme activities. For higher concentrations, it was observed that carbaryl has a depressive effect on mitochondrial respiration and on the generation of mitochondrial membrane potential, but with preservation of membrane integrity. A locus between Complex II and III appears particularly affected and the mitochondrial phosphorylation system relatively insensitive. Therefore, carbaryl inhibits mitochondrial respiration without affecting the phosphorylation complex. Carbaryl is toxic for mitochondria, although at concentrations higher as compared with other insecticide compounds. Mitochondrial toxicity should be excluded as one of the primary causes for carbaryl immediate toxicity, as concluded from the range of concentrations where carbaryl shows effective mitochondrial toxicity.