Rosanna Palumbo

Quercetin: A Pleiotropic Kinase Inhibitor Against Cancer

Increased consumption of fruits and vegetables can represent an easy strategy to significantly reduce the incidence of cancer. From this observation, derived mostly from epidemiological data, the new field of chemoprevention has emerged in the primary and secondary prevention of cancer. Chemoprevention is defined as the use of natural or synthetic compounds able to stop, reverse, or delay the process of tumorigenesis in its early stages. A large number of phytochemicals are potentially capable of simultaneously inhibiting and modulating several key factors regulating cell proliferation in cancer cells. Quercetin is a flavonoid possessing potential chemopreventive properties. It is a functionally pleiotropic molecule, possessing multiple intracellular targets, affecting different cell signaling processes usually altered in cancer cells, with limited toxicity on normal cells. Simultaneously targeting multiple pathways may help to kill malignant cells and slow down the onset of drug resistance. Among the different substrates triggered by quercetin, we have reviewed the ability of the molecule to inhibit protein kinases involved in deregulated cell growth in cancer cells.

Quercetin and anti-CD95(Fas/Apo1) enhance apoptosis in HPB-ALL cell line

Several malignant cell lines are resistant to CD95(Apo1/Fas)‐mediated apoptosis, even when the CD95 receptor is highly expressed. Sensitivity to CD95‐induced apoptosis can be restored using different molecules. In this study, we showed that quercetin, a naturally occurring flavonoid, in association with the agonistic anti‐CD95 monoclonal antibody, increases DNA fragmentation and caspase‐3 activity in HPB‐ALL cells. These cells have been selected for their known resistance to CD95‐induced apoptosis. At molecular level, quercetin lowers the level of intracellular reactive oxygen species, reduces mitochondrial transmembrane potential, thereby leaving the expression of CD95 receptor unchanged.

Flavonoid quercetin sensitizes a CD95-resistant cell line to apoptosis by activating protein kinase Cα

We previously demonstrated that quercetin, a naturally occurring flavonoid with strong antioxidant properties, was able to enhance programmed cell death in HPB-acute lymphoblastic leukemia (ALL) cell line, derived from a human tymoma, when associated with the agonistic anti-CD95 monoclonal antibody. Here, we report that HPB-ALL cells are normally resistant to CD95-mediated apoptosis, and quercetin is able to sensitize this cell line through a mechanism independent of its antioxidant properties. In fact, other compounds structurally and functionally similar to quercetin, when associated with anti-CD95 antibody did not induce any CD95-mediated apoptosis, still maintaining their antioxidant capacity. We found that quercetin effects are mediated by the activation of PKCα. Treatment of HPB-ALL cells with quercetin slightly decreased PKCα activity, but when the flavonoid was associated with anti-CD95, the kinase activity increased by 12-fold with respect to the treatment with quercetin. In addition, overexpression of PKCα induced programmed cell death in the absence of any additional stimulus, while a kinase-defective mutant of PKCα was ineffective. Our data confirm the involvement of specific PKC isoforms in CD95 signaling and suggest, for the first time, that quercetin targets this pathway increasing apoptogenic response in a cell line resistant to CD95-mediated apoptosis.

Antioxidant and cytotoxic properties of lyophilized beer extracts on HL-60 cell line

An impressive number of studies have suggested that red wine can be considered the protective beverage of choice against chronic and degenerative pathologies. Only few and controversial data are available on a potential, similar role for beer, which represents a more cost-effective, safe, and widely available beverage. Starting from the evidence that many antioxidant compounds present in red wine are also present at similar or even higher concentrations in beers, we first screened 48 commercially available beers and selected one (Mrt-HP) with very high polyphenol concentration and antioxidant activity estimated by ferric reducing antioxidant power. We demonstrated that a lyophilized preparation of Mrt-HP beer was cytotoxic with respect to a beer with low polyphenolic content (Trt-LP) when assayed on HL-60 human leukemia cell line. We measured a 60% decrease in cell viability at a polyphenol concentration of 250 μM quercetin equivalents. We also demonstrated that Mrt-HP cytotoxicity was not an artifact due to cell growth conditions because addition of Mrt-HP extracts to cell medium generated peroxide levels indistinguishable from controls. By means of cytofluorimetric analysis of pre-G1 population and caspase 3 activation, we demonstrated that Mrt-HP extracts activated apoptosis in HL-60 cell line. Finally, we found that the concentration of quercetin, resveratrol, and gallic acid in Mrt-HP was 10, 4.6, and 4.6-fold higher, respectively, than in Trt-LP, suggesting that the presence of these molecules might be responsible for the observed cytotoxicity. These data, together with the low in vivo beer toxicity reported in the literature, suggest a possible chemopreventive role for this beverage that requires further studies in animal models.

Target selective micelles for bombesin receptors incorporating Au(III)-dithiocarbamato complexes

Pure sterically stabilized micelles (SSM) of DSPE-PEG2000, and sterically stabilized mixed micelles (SSMM) containing PC or DOPC phospholipids (5, 10 or 20% mol/mol with respect to DSPE-PEG2000) are developed as delivery systems for the gold based cytotoxic drug Au(III)-dithiocarbamato complex AuL12. In particular, SSMM containing 5% of PC at 5mM of lipid concentration encapsulates 61.0 μg of AuL12 with a DL% of 1.13. The gold complex remains stable up to 72 h when incorporated in the aggregate, as indicated by UV-vis measurements. Incorporation in micelle composition of a low amount of the peptide derivative MonY-BN-AA1, containing a bombesin peptide analogue does not influence structural parameters of the micelles (diameter around 20 nm) neither the AuL12 loading parameters. Target selective properties of the peptide containing full aggregate on PC-3 cells overexpressing the GRP/bombesin receptors are observed by in vitro cytotoxic studies: a decrease of cell viability, ∼ 50%, is obtained in cells treated with AuL12-targeted micelles at 10 μM drug concentration for 48 h with respect to untargeted micelles.

VEGFR1D2 in drug discovery: Expression and molecular characterization

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor. Its biological activity is mediated by the binding to the extracellular domain of two tyrosine kinase transmembrane receptors: VEGFR1 and VEGFR2. Deletion studies showed that VEGF binding site resides in the first three domains of VEGFR1 and in domains 2 and 3 of VEGFR2. In particular, the second extracellular domain of VEGFR1 (VEGFR1(D2)) contains most of the VEGF binding requirements. Here, we report an efficient expression protocol and the molecular characterization by spectroscopic techniques of VEGFR1(D2). The protein was expressed in E. coli and refolded from inclusion bodies. The recombinant protein assumes the correct fold as assessed by a combination of biochemical and functional assays as well as by NMR characterization. Furthermore, the recombinant VEGFR1(D2) was analyzed by circular dichroism and fluorescence spectroscopy. The protein obtained by this procedure is suitable for the structural characterization of the complexes with receptor binders and to be used in interaction/screening studies.

Peptide-labeled supramolecular aggregates as selective doxorubicin carriers for delivery to tumor cells.

New liposomal aggregates, prepared by combining together, in a 90:10 molar ratio, two amphiphilic monomers, one containing two hydrocarbon chains in the hydrophobic region and the anionic DOTA chelating agent as hydrophilic moiety, and the other containing the same hydrophobic moiety and the CCK8 peptide, are described. The liposomal aggregates because of the presence of the specific moiety, constituted by the CCK8 peptide, which selectively recognizes CCK receptors on tumor cells are used as drug carriers with the aim to deliver into tumor cells the appropriate antitumor drug. The drug loading content and the releasing properties of the liposomal aggregates are studied by the use of the cytotoxic doxorubicin as drug model. The doxorubicin loading content determination reveals that above 95% of the total drug was uptaken with a corresponding drug/lipid w/w ratio of 0.134. The cellular uptake of the targeted liposomal doxorubicin with respect to the self‐assembled, nonspecific, liposomal doxorubicin is evaluated using flow cytometry assays. The doxorubicin cell content for two types of cell systems, namely, A431 and HuVEC cells, for peptide derivatized liposomes was 70‐ and 8‐fold higher, respectively, than for nontargeted liposomes, indicating that the bioactive CCK8 peptide is able to enhance the doxorubicin uptake into the carcinoma cells in vitro. The cytotoxicity effect of liposomal doxorubicin on A431 cells has been assessed by MTT assays: in presence of drug amounts ranged between 250 and 1000 ng/ml, incubation with peptide derivatized liposomes showed significantly lower cell survival compared with nontargeted liposomes.

Liposomal doxorubicin doubly functionalized with CCK8 and R8 peptide sequences for selective intracellular drug delivery

A new dual‐ligand liposomal doxorubicin delivery system, which couples targeting to enhanced cellular uptake and may lead to a more efficient drug delivery system, is here designed and synthetized. Liposomes based on the composition 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine/1,2‐distearoyl‐sn‐glycero‐3‐phosphoethanolamine‐Peg2000‐R8/(C18)2‐L5‐SS‐CCK8 (87/8/5 mol/mol/mol) were prepared and loaded with doxorubicin. Presence of the two peptides on the external surface is demonstrated by fluorescence resonance energy transfer assay. The combination of the R8 cell‐penetrating peptide and of the CCK8 targeting peptide (homing peptide) on the liposome surface is obtained by combining pre‐modification and post‐modification methods. In the dual‐ligand system, the CCK8 peptide is anchored to the liposome surface by using a disulfide bond. This chemical function is inserted in order to promote the selective cleavage of the homing peptide under the reductive conditions expected in proximity of the tumor site, thus allowing targeting and internalization of the liposomal drug. Copyright

Isolation and characterization of human embryonic osteoblasts

SummaryHuman osteoblasts were obtained by migration and proliferation of cells from embryonic membranous bone on glass fragments. Light and electron microscopy analyses revealed a typical osteoblast-like appearance with high protein synthesis activity. The cells showed high alkaline phosphatase activity that was associated with plasma membranes and matrix vesicles and was 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] responsive. In contrast to the adult osteoblasts, embryonic cells could not produce detectable levels of osteocalcin, not even in the presence of 1,25(OH)2D3. Osteoblasts grown in multilayers produced a thick extracellular matrix, mainly composed of type I collagen, that mineralized in the presence of 10 mM β-glycerophosphate. Because of their intrinsic osteogenic capacity, embryonic osteoblasts represent a valuable model for studying the mineralization process in vitro. In addition, the embryonic origin of these cells renders them a precious experimental system for the elucidation of mechanisms at the basis of differentiation of osteoblastic lineage.

C-terminal truncation of Vascular Endothelial Growth Factor mimetic helical peptide preserves structural and receptor binding properties

Vascular Endothelial Growth Factor mimetic peptides have interesting applications in therapeutic angiogenesis. Recently, we described the proangiogenic properties of a 15 mer peptide designed on the N-terminal helix 17-25 of VEGF. The peptide was stabilized introducing well known peptide chemical tools among which N- and C-terminal capping sequence. Here, we show that the C-terminal sequence does not affect the structural and biological properties of the full-length peptide. In fact, a C-terminal truncated analog peptide resulted in a well folded and stable helix retaining the ability to bind to VEGF receptors. This study will allow to develop smaller peptidomimetic analogs able to modulate the VEGF-dependent angiogenesis.