The discovery of indolone GW5074 during a comprehensive search for non-polyamine-based polyamine transport inhibitors

The native polyamines putrescine, spermidine, and spermine are essential for cell development and proliferation. Polyamine levels are often increased in cancer tissues and polyamine depletion is a validated anticancer strategy. Cancer cell growth can be inhibited by the polyamine biosynthesis inhibitor difluoromethylornithine (DFMO), which inhibits ornithine decarboxylase (ODC), the rate-limiting enzyme in the polyamine biosynthesis pathway. Unfortunately, cells treated with DFMO often replenish their polyamine pools by importing polyamines from their environment. Several polyamine-based molecules have been developed to work as polyamine transport inhibitors (PTIs) and have been successfully used in combination with DFMO in several cancer models. Here, we present the first comprehensive search for potential non-polyamine based PTIs that work in human pancreatic cancer cells in vitro. After identifying and testing five different categories of compounds, we have identified the c-RAF inhibitor, GW5074, as a novel non-polyamine based PTI. GW5074 inhibited the uptake of all three native polyamines and a fluorescent-polyamine probe into human pancreatic cancer cells. GW5074 significantly reduced pancreatic cancer cell growth in vitro when treated in combination with DFMO and a rescuing dose of spermidine. Moreover, GW5074 alone reduced tumor growth when tested in a murine pancreatic cancer mouse model in vivo. In summary, GW5074 is a novel non-polyamine-based PTI that potentiates the anticancer activity of DFMO in pancreatic cancers.

Tissue-specific regulation of potassium homeostasis by high doses of cationic amino acids

The administration of l-arginine hydrochloride has been used for testing pituitary secretion in humans, and as an experimental model for induction of acute pancreatitis in rats and mice. Whereas in the first case, the administration of the amino acid is associated with hiperkalemia, in the model of acute pancreatitis no data are available on possible changes in potassium homeostasis. The present study shows that the acute administration to mice of l-arginine hydrochloride or other cationic amino acids almost duplicate plasma potassium levels. This effect was associated to a marked decrease of tissue potassium in both pancreas and liver. No changes were found in other tissues. These changes cannot be ascribed to the large load of chloride ions, since similar effects were produced when l-ornithine aspartate was administered. The changes in potassium levels were dependent on the dose. The displacement of intracellular potassium from the liver and pancreas to the extracellular compartment appears to be dependent on the entry of the cationic amino acid, since the administration of an equivalent dose of alfa-difluoromethyl ornithine HCl (DFMO), a non physiological analog of l-ornithine, which is poorly taken by the tissues in comparison with the physiological cationic amino acids, did not produce any change in potassium levels in pancreas and liver. The analyses of the expression of cationic amino acid transporters (CAT) suggest that the CAT-2 transporter may be implicated in the potassium/cationic amino acid interchange in liver and pancreas. The possible physiological or pathological relevance of these findings is discussed.

Metabolomics of adherent mammalian cells by capillary electrophoresis-mass spectrometry: HT-29 cells as case study

In this work, the optimization of an effective protocol for cell metabolomics is described with special emphasis in the sample preparation and subsequent analysis of intracellular metabolites from adherent mammalian cells by capillary electrophoresis-mass spectrometry. As case study, colon cancer HT-29 cells, a human cell model to investigate colon cancer, are employed. The feasibility of the whole method for cell metabolomics is demonstrated via a fast and sensitive profiling of the intracellular metabolites HT-29 cells by capillary electrophoresis-time-of-flight mass spectrometry (CE-TOF MS). The suitability of this methodology is further corroborated through the examination of the metabolic changes in the polyamines pathway produced in colon cancer HT-29 cells by difluoromethylornithine (DFMO), a known potent ornithine decarboxylase inhibitor. The selection of the optimum extraction conditions allowed a higher sample volume injection that led to an increase in CE-TOF MS sensitivity. Following a non-targeted metabolomics approach, 10 metabolites (namely, putrescine, ornithine, gamma-aminobutyric acid (GABA), oxidized and reduced glutathione, 5'-deoxy-5'-(methylthio)adenosine, N-acetylputrescine, cysteinyl-glycine, spermidine and an unknown compound) were found to be significantly altered by DFMO (p<0.05) in HT-29 cells. In addition to the effect of DFMO on polyamine metabolism, minor modifications of other metabolic pathways (e.g., related to intracellular thiol redox state) were observed.

A quantitative proteomic screen to identify potential drug resistance mechanism in α-difluoromethylornithine (DFMO) resistant Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani is a systemic protozoan disease that is fatal if left untreated. The promastigote form of L. donovani is sensitive to growth inhibition by dl-α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), the first enzyme of the polyamine biosynthetic pathway. Exposure of a wild type (DI700) cell population to gradually increasing concentrations of DFMO resulted in the selection of a strain of Leishmania (DFMO-16), which was capable of proliferating in 16mM DFMO. To elucidate the molecular basis for this resistance, we undertook a comparative proteomic analysis of DFMO-resistant/sensitive parasites using isobaric tagging for relative and absolute quantification (iTRAQ/LC-MS/MS). Out of the 101 proteins identified in at least 2 of the 3 independent experiments, 82 proteins are 1.5- to 44.0-fold more abundant in DFMO-resistant strain (DFMO-16) while 19 are 2- to 5.0-fold less abundant as compared to the wild-type (DI700) parasites. Proteins with 2-fold or greater abundance in the DFMO-resistant strain include free radical detoxification, polyamine and trypanothione metabolic proteins, proteins involved in metabolism, intracellular survival and proteolysis, elongation factors, signaling molecules and mitochondrial transporters, and many with no annotated function. Differentially modulated proteins contribute to our understanding of molecular mechanism of DFMO-resistance and have the potential to act as biomarkers.

BIOLOGICAL SIGNIFICANCE

This study will facilitate a deeper understanding of the phenomenon of acquired drug resistance and possible biomarkers in Leishmania against antiparasitic drug DFMO. Also it will provide information about the metabolic pathways modulated in resistant parasites as an adaptation mechanism to counter drugs. Studies like this are important to safeguard the efficacy of a limited repertoire of anti-parasitic drugs, and to lead the development of new drugs and drug combinations.