Félix A. Urra

Selective Vulnerability of Cancer Cells by Inhibition of Ca2+ Transfer from Endoplasmic Reticulum to Mitochondria

In the absence of low-level ER-to-mitochondrial Ca(2+) transfer, ATP levels fall, and AMPK-dependent, mTOR-independent autophagy is induced as an essential survival mechanism in many cell types. Here, we demonstrate that tumorigenic cancer cell lines, transformed primary human fibroblasts, and tumors in vivo respond similarly but that autophagy is insufficient for survival, and cancer cells die while their normal counterparts are spared. Cancer cell death is due to compromised bioenergetics that can be rescued with metabolic substrates or nucleotides and caused by necrosis associated with mitotic catastrophe during their proliferation. Our findings reveal an unexpected dependency on constitutive Ca(2+) transfer to mitochondria for viability of tumorigenic cells and suggest that mitochondrial Ca(2+) addiction is a feature of cancer cells.

Mitochondria: A Promising Target for Anticancer Alkaloids

A great number of alkaloids exhibit high potential in cancer research. Some of them are anticancer drugs with well-defined clinical uses, exerting their action on microtubules dynamics or DNA replication and topology. On the other hand, mitochondria have been recognized as an essential organelle in the establishment of tumor characteristics, especially the resistance to cell death, high proliferative capacity and adaptation to unfavorable cellular environment. Interestingly, many alkaloids exert their anticancer activities affecting selectively some functions of the tumor mitochondria by 1) modulating OXPHOS and ADP/ATP transport, 2) increasing ROS levels and mitochondrial potential dissipation by crosstalk between endoplasmic reticulum (ER) and mitochondria, 3) inducing mitochondria-dependent apoptosis and autophagy, 4) inhibiting mitochondrial metabolic pathways and 5) by alteration of the morphology and biogenesis of this organelle. These antecedents show the relevance of developing research about the effects of alkaloids on functions controlled by tumor mitochondria, offering an attractive target for the design of new alkaloid derivatives, considering organelle- specific delivery strategies. This review describes mitochondria as a central component in the anticancer action of a set of alkaloids, in a way to illustrate the importance of this organelle in medicinal chemistry.

An ortho-carbonyl substituted hydroquinone derivative is an anticancer agent that acts by inhibiting mitochondrial bioenergetics and by inducing G2/M-phase arrest in mammary adenocarcinoma TA3

Tumor cells present a known metabolic reprogramming, which makes them more susceptible for a selective cellular death by modifying its mitochondrial bioenergetics. Anticancer action of the antioxidant 9,10-dihydroxy-4,4-dimethyl-5,8-dihydroanthracen-1(4H)-one (HQ) on mouse mammary adenocarcinoma TA3, and its multiresistant variant TA3-MTXR, were evaluated. HQ decreased the viability of both tumor cells, affecting slightly mammary epithelial cells. This hydroquinone blocked the electron flow through the NADH dehydrogenase (Complex I), leading to ADP-stimulated oxygen consumption inhibition, transmembrane potential dissipation and cellular ATP level decrease, without increasing ROS production. Duroquinol, an electron donor at CoQ level, reversed the decrease of cell viability induced by HQ. Additionally, HQ selectively induced G₂/M-phase arrest. Taken together, our results suggest that the bioenergetic dysfunction provoked by HQ is implicated in its anticancer action.

The Paraguayan Rhinella toad venom: Implications in the traditional medicine and proliferation of breast cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE Toads belonging to genus Rhinella are used in Paraguayan traditional medicine to treat cancer and skin infections. AIM OF THE STUDY The objective of the study was to determine the composition of venoms obtained from three different Paraguayan Rhinella species, to establish the constituents of a preparation sold in the capital city of Paraguay to treat cancer as containing the toad as ingredient, to establish the effect of the most active Rhinella schneideri venom on the cell cycle using human breast cancer cells and to assess the antiprotozoal activity of the venoms. METHODS The venom obtained from the toads parotid glands was analyzed by HPLC-MS-MS. The preparation sold in the capital city of Paraguay to treat cancer that is advertised as made using the toad was analyzed by HPLC-MS-MS. The effect of the R. schneideri venom and the preparation was investigated on human breast cancer cells. The antiprotozoal activity was evaluated on Leishmania braziliensis, L. infantum and murine macrophages. RESULTS From the venoms of R. ornata, R. schneideri and R. scitula, some 40 compounds were identified by spectroscopic and spectrometric means. Several minor constituents are reported for the first time. The preparation sold as made from the toad did not contained bufadienolides or compounds that can be associated with the toad but plant compounds, mainly phenolics and flavonoids. The venom showed activity on human breast cancer cells and modified the cell cycle proliferation. The antiprotozoal effect was higher for the R. schneideri venom and can be related to the composition and relative ratio of constituents compared with R. ornata and R. scitula. CONCLUSIONS The preparation sold in the capital city of Paraguay as containing the toad venom, used popularly to treat cancer did not contain the toad venom constituents. Consistent with this, this preparation was inactive on proliferation of human breast cancer cells. In contrast, the toad venoms of Rhinella species altered the cell cycle progression, affecting the proliferation of malignant cells. The findings suggest that care should be taken with the providers of the preparation and that the crude drug present a strong activity towards human breast cancer cell lines. The antiprotozoal effect of the R. schneideri venom was moderate while the venom of R. ornata was devoid of activity and that of R. scitula was active at very high concentration.

Two new species of the Liolaemus elongatus-kriegi complex (Iguania, Liolaemidae) from Andean highlands of southern Chile

Abstract The elongatus-kriegi complex is one of the most diverse clades of the Liolaemus (sensu stricto) subgenus of lizards. There are currently 29 species recognized in this group distributed between Chile and Argentina. Based on molecular evidence, there seem to be five main clades nested within this complex: the elongatus, leopardinus, kriegi, petrophilus and punmahuida clades. Liolaemus buergeri and Liolaemus kriegi, both of the kriegi clade, were believed to inhabit the surroundings of the Laja Lagoon, in the Biobío Region of Chile. Moreover, this Chilean population of Liolaemus kriegi was recently recognized as an undescribed taxon called “Liolaemus sp. A” based on molecular phylogenetics. In this work, we studied these two populations of the Laja Lagoon and provided the morphological diagnosis to describe them as two new species: Liolaemus scorialis sp. n. and Liolaemus zabalai sp. n., previously considered Liolaemus buergeri and “Liolaemus kriegi/Liolaemus sp. A” respectively. Additionally, we identified another population of Liolaemus scorialis in the vicinity of La Mula Lagoon in the Araucanía Region of Chile. Liolaemus scorialis differs from almost all of the species of the elongatus-kriegi complex by its considerably smaller size. Nevertheless, without molecular data we cannot assign it to any particular subclade. Liolaemus zabalai belongs to the kriegi clade based on published molecular phylogenies. Finally, we provide some natural history data on both species and we document for the first time the presence of Liolaemus neuquensis in Chile from a museum specimen from La Mula Lagoon.

Targeting Metastasis with Snake Toxins: Molecular Mechanisms

Metastasis involves the migration of cancer cells from a primary tumor to invade and establish secondary tumors in distant organs, and it is the main cause for cancer-related deaths. Currently, the conventional cytostatic drugs target the proliferation of malignant cells, being ineffective in metastatic disease. This highlights the need to find new anti-metastatic drugs. Toxins isolated from snake venoms are a natural source of potentially useful molecular scaffolds to obtain agents with anti-migratory and anti-invasive effects in cancer cells. While there is greater evidence concerning the mechanisms of cell death induction of several snake toxin classes on cancer cells; only a reduced number of toxin classes have been reported (i.e., disintegrins/disintegrin-like proteins, C-type lectin-like proteins, C-type lectins, serinproteases, cardiotoxins, snake venom cystatins) as inhibitors of adhesion, migration, and invasion of cancer cells. Here, we discuss the anti-metastatic mechanisms of snake toxins, distinguishing three targets, which involve (1) inhibition of extracellular matrix components-dependent adhesion and migration, (2) inhibition of epithelial-mesenchymal transition, and (3) inhibition of migration by alterations in the actin/cytoskeleton network.

The Mitochondrial Complex(I)ty of Cancer

Recent evidence highlights that the cancer cell energy requirements vary greatly from normal cells and that cancer cells exhibit different metabolic phenotypes with variable participation of both glycolysis and oxidative phosphorylation. NADH–ubiquinone oxidoreductase (Complex I) is the largest complex of the mitochondrial electron transport chain and contributes about 40% of the proton motive force required for mitochondrial ATP synthesis. In addition, Complex I plays an essential role in biosynthesis and redox control during proliferation, resistance to cell death, and metastasis of cancer cells. Although knowledge about the structure and assembly of Complex I is increasing, information about the role of Complex I subunits in tumorigenesis is scarce and contradictory. Several small molecule inhibitors of Complex I have been described as selective anticancer agents; however, pharmacologic and genetic interventions on Complex I have also shown pro-tumorigenic actions, involving different cellular signaling. Here, we discuss the role of Complex I in tumorigenesis, focusing on the specific participation of Complex I subunits in proliferation and metastasis of cancer cells.

Determinants of Anti-Cancer Effect of Mitochondrial Electron Transport Chain Inhibitors: Bioenergetic Profile and Metabolic Flexibility of Cancer Cells

Recent evidence highlights that energy requirements of cancer cells vary greatly from normal cells and they exhibit different metabolic phenotypes with variable participation of both glycolysis and oxidative phosphorylation (OXPHOS). Interestingly, mitochondrial electron transport chain (ETC) has been identified as an essential component in bioenergetics, biosynthesis and redox control during proliferation and metastasis of cancer cells. This dependence converts ETC of cancer cells in a promising target to design small molecules with anti-cancer actions. Several small molecules have been described as ETC inhibitors with different consequences on mitochondrial bioenergetics, viability and proliferation of cancer cells, when the substrate availability is controlled to favor either the glycolytic or OXPHOS pathway. These ETC inhibitors can be grouped as 1) inhibitors of a respiratory complex (e.g. rotenoids, vanilloids, alkaloids, biguanides and polyphenols), 2) inhibitors of several respiratory complexes (e.g. capsaicin, ME-344 and epigallocatechin-3 gallate) and 3) inhibitors of ETC activity (e.g. elesclomol and VLX600). Although pharmacological ETC inhibition may produce cell death and a decrease of proliferation of cancer cells, factors such as degree of inhibition of ETC activity by small molecules, bioenergetic profile and metabolic flexibility of different cancer types or subpopulations of cells in a particular cancer type, can affect the impact of the anti-cancer actions. Particularly interesting are the adaptive mechanisms induced by ETC inhibition, such as induction of glutamine-dependent reductive carboxylation, which may offer a strategy to sensitize cancer cells to inhibitors of glutamine metabolism.

FR58P1a; a new uncoupler of OXPHOS that inhibits migration in triple-negative breast cancer cells via Sirt1/AMPK/β1-integrin pathway

Highly malignant triple-negative breast cancer (TNBC) cells rely mostly on glycolysis to maintain cellular homeostasis; however, mitochondria are still required for migration and metastasis. Taking advantage of the metabolic flexibility of TNBC MDA-MB-231 cells to generate subpopulations with glycolytic or oxidative phenotypes, we screened phenolic compounds containing an ortho-carbonyl group with mitochondrial activity and identified a bromoalkyl-ester of hydroquinone named FR58P1a, as a mitochondrial metabolism-affecting compound that uncouples OXPHOS through a protonophoric mechanism. In contrast to well-known protonophore uncoupler FCCP, FR58P1a does not depolarize the plasma membrane and its effect on the mitochondrial membrane potential and bioenergetics is moderate suggesting a mild uncoupling of OXPHOS. FR58P1a activates AMPK in a Sirt1-dependent fashion. Although the activation of Sirt1/AMPK axis by FR58P1a has a cyto-protective role, selectively inhibits fibronectin-dependent adhesion and migration in TNBC cells but not in non-tumoral MCF10A cells by decreasing β1-integrin at the cell surface. Prolonged exposure to FR58P1a triggers a metabolic reprograming in TNBC cells characterized by down-regulation of OXPHOS-related genes that promote cell survival but comprise their ability to migrate. Taken together, our results show that TNBC cell migration is susceptible to mitochondrial alterations induced by small molecules as FR58P1a, which may have therapeutic implications.

Phymaturus vociferator Pincheira-Donoso, 2004 (Squamata: Liolaemidae): new records and updated geographic distribution

Phymaturus vociferator Pincheira-Donoso 2004 was known until now only from type locality, Laguna del Laja, Biobio Region, Chile. Here, we report new records in the vicinity of Termas de Chillan and extend this species’ distribution 58.3 km north of its type locality.