Matteo Romio

Improving the Efficacy of Plant Polyphenols

Plant polyphenols exhibit potentially useful effects in a wide variety of pathophysiological settings. They interact with proteins such as signalling kinases, transcription factors and ion channels, and modulate redox processes, such as those taking place in mitochondria. Biomedical applications of these natural compounds are however severely hindered by their low bioavailability, rapid metabolism, and often by unfavourable physico-chemical properties, e.g. a generally low water solubility. Derivatives are under development with the aim of improving their bioavailability and/or bioefficacy. Various strategies can be adopted. An increase in circulating blood levels of non-metabolized natural compound may be attainable through prodrugs. In the ideal prodrug, phenolic hydroxyls are protected by capping groups which a) help or at least do not hinder permeation of epithelia; b) prevent conjugative modifications during absorption and first-pass through the liver; c) are eliminated with opportune kinetics to regenerate the parent compound. Moreover, prodrugs may be designed with the goals of modulating physical properties of the parent compound, and/or changing its distribution in the body. A more specific action may be achieved by concentrating the compounds at specific sites of action. An example of the second approach is represented by mitochondria-targeted redox-active polyphenol derivatives, designed to intervene on radical processes in these organelles and as a tool either to protect cells from oxidative insults or to precipitate their death. Mitochondrial targeting can be achieved through conjugation with a triphenylphosphonium lipophilic cation. Quercetin and resveratrol were chosen as model polyphenols for these proof-of-concept studies. Data available at the moment show that both quercetin and resveratrol mitochondria-targeted derivatives are pro-oxidant and cytotoxic in vitro, selectively killing fast-growing and tumoural cells when supplied in the low μM range; the mechanism of ROS generation appears to differ between the two classes of compounds. These approaches are emerging as promising strategies to obtain new efficient chemopreventive and/or chemotherapeutic drugs based on polyphenols derivatives.

New natural amino acid-bearing prodrugs boost pterostilbene’s oral pharmacokinetic and distribution profile

&NA; The biomedical effects of the natural phenol pterostilbene are of great interest but its bioavailability is negatively affected by the phenolic group in position 4′ which is an ideal target for the conjugative enzymes of phase II metabolism. We report the synthesis and characterization of prodrugs in which the hydroxyl moiety is reversibly protected as a carbamate ester linked to the N‐terminus of a natural amino acid. Prodrugs comprising amino acids with hydrophobic side chains were readily absorbed after intragastric administration to rats. The Area Under the Curve for pterostilbene in blood was optimal when prodrugs with isoleucine or &bgr;‐alanine were used. The prodrug incorporating isoleucine was used for further studies to map distribution into major organs. When compared to pterostilbene itself, administration of the isoleucine prodrug afforded increased absorption, reduced metabolism and higher concentrations of pterostilbene, sustained for several hours, in most of the organs examined. Experiments using Caco‐2 cells as an in vitro model for human intestinal absorption suggest that the prodrug could have promising absorption profiles also in humans; its uptake is partly due to passive diffusion, and partly mediated by H+‐dependent transporters expressed on the apical membrane of enterocytes, such as PepT1 and OATP. Graphical abstract Figure. No caption available.

Resveratrol derivatives as a pharmacological tool

Prodrugs of resveratrol are under development. Among the long‐term goals, still largely elusive, are (1) modulating physical properties (e.g., water‐soluble derivatives bearing polyethylene glycol chains), (2) changing distribution in the body (e.g., galactosyl derivatives restricted to the intestinal lumen), (3) increasing absorption from the gastrointestinal tract (e.g., derivatives imitating the natural substrates of endogenous transporters), and (4) hindering phase II metabolism (e.g., temporarily blocking the hydroxyls), all contributing to (5) increasing bioavailability. The chemical bonds that have been tested for functionalization include carboxyester, acetal, and carbamate groups. A second approach, which can be combined with the first, seeks to reinforce or modify the biochemical activities of resveratrol by concentrating the compound at specific subcellular sites. An example is provided by mitochondria‐targeted derivatives. These proved to be pro‐oxidant and cytotoxic in vitro, selectively killing fast‐growing and tumor cells when supplied in the low micromolar range. This suggests the possibility of anticancer applications.

Regulation of Proliferation by a Mitochondrial Potassium Channel in Pancreatic Ductal Adenocarcinoma Cells

Previous results link the mitochondrial potassium channel Kv1.3 (mitoKv1.3) to the regulation of apoptosis. By synthesizing new, mitochondria-targeted derivatives (PAPTP and PCARBTP) of PAP-1, a specific membrane-permeant Kv1.3 inhibitor, we have recently provided evidence that both drugs acting on mitoKv1.3 are able to induce apoptosis and reduce tumor growth in vivo without affecting healthy tissues and cells. In the present article, by exploiting these new drugs, we addressed the question whether mitoKv1.3 contributes to the regulation of cell proliferation as well. When used at low concentrations, which do not compromise cell survival, both drugs slightly increased the percentage of cells in S phase while decreased the population at G0/G1 stage of cells from two different pancreatic ductal adenocarcinoma lines. Our data suggest that the observed modulation is related to ROS levels within the cells, opening the way to link mitochondrial ion channel function to downstream, ROS-related signaling events that might be important for cell cycle progression.

Novel Mitochondria-Targeted Furocoumarin Derivatives as Possible Anti-Cancer Agents

Targeting small molecules to appropriate subcellular compartments is a way to increase their selectivity and effectiveness while minimizing side effects. This can be accomplished either by stably incorporating specific “homing” properties into the structure of the active principle, or by attaching to it a targeting moiety via a labile linker, i.e., by producing a “targeting pro-drug.” Mitochondria are a recognized therapeutic target in oncology, and blocking the population of the potassium channel Kv1.3 residing in the inner mitochondrial membrane (mtKv1.3) has been shown to cause apoptosis of cancerous cells expressing it. These concepts have led us to devise novel, mitochondria-targeted, membrane-permeant drug candidates containing the furocoumarin (psoralenic) ring system and the triphenylphosphonium (TPP) lipophilic cation. The strategy has proven effective in various cancer models, including pancreatic ductal adenocarcinoma, melanoma, and glioblastoma, stimulating us to devise further novel molecules to extend and diversify the range of available drugs of this type. New compounds were synthesized and tested in vitro; one of them—a prodrug in which the coumarinic moiety and the TPP group are linked by a bridge comprising a labile carbonate bond system—proved quite effective in in vitro cytotoxicity assays. Selective death induction is attributed to inhibition of mtKv1.3. This results in oxidative stress, which is fatal for the already-stressed malignant cells. This compound may thus be a candidate drug for the mtKv1.3-targeting therapeutic approach.