Biomedical subjects

Pier Giovanni Baraldi

Publications and source records attributed to Pier Giovanni Baraldi.

At least 37 records · Page 2Linked to original sources

PubMed2005

Combined target-based and ligand-based drug design approach as a tool to define a novel 3D-pharmacophore model of human A3 adenosine receptor antagonists: pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine derivatives as a key study.

A combined target-based and ligand-based drug design approach has been carried out to define a novel pharmacophore model of the human A(3) receptor antagonists. High throughput molecular docking and comparative molecular field analysis (CoMFA) have been used in tandem to assemble a new target based pharmacophore model. In parallel, to provide more accurate information about the putative binding site of these A(3) inhibitors, a rhodopsin-based model of the human A(3) receptor was built and a novel Y-shape binding motif has been proposed. Docking-based structure superimposition has been used to perform a quantitative study of the structure-activity relationships for binding of these pyrazolo-triazolo-pyrimidines to adenosine A(3) receptor using CoMFA. Both steric and the electrostatic contour plots obtained from the CoMFA analysis nicely fit on the hypothetical binding site obtained by molecular docking. On the basis of the combined hypothesis, we have designed, synthesized, and tested 17 new derivatives. Consistently, the predicted K(i) values were very close to the experimental values.

Adenosine A3 Receptor Antagonists↗

PubMed2005

New heterocyclic ligands for the adenosine receptors P1 and for the ATP receptors P2.

Extracellular adenosine and adenine nucleotides induce various cellular responses through activation of P1 and P2 receptors. P1 receptors preferentially recognize adenosine and four different G protein-coupled receptors (A(1), A(2A), A(2B), and A(3) subtypes) have been identified. On the other hand, P2 receptors are activated by adenine and/or uridine nucleotides and classified into two families: ionotropic P2X and G protein-coupled P2Y receptors. In this article, we summarize our studies which led to development of new potent and selective heterocyclic ligands for the adenosine receptors P1 and for the ATP receptors P2X(7).

Adenine Nucleotides↗

PubMed2005

A3 adenosine receptors modulate hypoxia-inducible factor-1alpha expression in human A375 melanoma cells.

Hypoxia-inducible factor-1 (HIF-1) is a key regulator of genes crucial to many aspects of cancer biology. The purine nucleoside, adenosine, accumulates within many tissues under hypoxic conditions, including that of tumors. Because the levels of both HIF-1 and adenosine are elevated within the hypoxic environment of solid tumors, we investigated whether adenosine may regulate HIF-1. Here we show that, under hypoxic conditions (< 2% O2), adenosine upregulates HIF-1alpha protein expression in a dose-dependent and time-dependent manner, exclusively through the A3 receptor subtype. The response to adenosine was generated at the cell surface because the inhibition of A3 receptor expression, by using small interfering RNA, abolished nucleoside effects. A3 receptor stimulation in hypoxia also increases angiopoietin-2 (Ang-2) protein accumulation through the induction of HIF-1alpha. In particular, we found that A3 receptor stimulation activates p44/p42 and p38 mitogen-activated protein kinases, which are required for A3-induced increase of HIF-1alpha and Ang-2. Collectively, these results suggest a cooperation between hypoxic and adenosine signals that ultimately may lead to the increase in HIF-1-mediated effects in cancer cells.

Adenosine↗

PubMed2005

Pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine ligands, new tools to characterize A3 adenosine receptors in human tumor cell lines.

Increased concentrations of extracellular adenosine are reached in ischemic or inflamed tissues but have also been detected inside tumoral masses. If this finding may account for an important role of adenosine in the pathogenesis of tumors remains to be determined in view of its contradictory effects on cell survival and proliferation. In particular, adenosine was found to exert its effects on proliferation and on cell death mainly through the A(3) adenosine receptor. Therefore, a complete pharmacological characterization of the subtype and number of the expressed A(3) adenosine receptors is necessary for the elucidation of the role of adenosine via A(3) receptors in a specific cell subtype. The lack of potent and selective radiolabelled A(3) receptor antagonists has been, in the past, the major obstacle in the characterization of structure, function and regulation of this adenosine receptor subtype. Recently, our group has identified a series of substituted pyrazolotriazo-lopyrimidine derivatives as potent and selective antagonists to human A(3) adenosine receptors. The most recent results obtained in this field will be summarized in the present review. Furthermore, the review will report the results of the biochemical and pharmacological characterization of A(3) receptors in different human tumor cell lines and the multiple A(3) receptor-sustained ways that could prime tumor development.

Adenosine A3 Receptor Antagonists↗

PubMed2005

Leukocyte P2 receptors: a novel target for anti-inflammatory and anti-tumor therapy.

P2 receptors are a class of plasma membrane receptors ligated by extracellular nucleotides and expressed ubiquitously throughout the body. Two main families are known: P2X and P2Y. P2X are ligand (ATP)-gated channels, while P2Y are G-protein-coupled seven membrane-spanning receptors. The P2X and the P2Y subfamilies comprise seven and eight members, respectively. While ATP is the only known physiological ligand of P2X receptors, P2Y receptors are known to be also activated by ADP, UTP, UDP and UDP-glucose in a subtype-specific manner. Several P2 subtypes are expressed by leukocytes where they have been implicated in a host of different responses ranging from chemotaxis to differentiation, from proliferation to cytotoxicity, from secretion of inflammatory mediators to cell fusion. However, until recently there was no in vivo proof of the participation of P2 receptors in inflammatory or proliferative disorders and, in addition, few pharmacological modulators of P2 function were available. During the last two years animal and human studies have produced preliminary but nevertheless compelling evidence in support of an important function of P2 receptors in inflammation and hematological tumors. Importantly, selective blockers of these receptors have been synthesized, thus paving the way to the possible development of P2-targeted anti-inflammatory and anti-tumoral therapies.

Anti-Inflammatory Agents↗

PubMed2004

Synthesis, radiolabeling, and preliminary biological evaluation of [3H]-1-[(S)-N,O-bis-(isoquinolinesulfonyl)-N-methyl-tyrosyl]-4-(o-tolyl)-piperazine, a potent antagonist radioligand for the P2X7 receptor.

The design, synthesis, and preliminary biological evaluation of the first potent radioligand antagonist for the P2X(7) receptor, named [(3)H]-1-[(S)-N,O-bis-(isoquinolinesulfonyl)-N-methyl-tyrosyl]-4-(o-tolyl)-piperazine (compound 13), are reported. This compound bound to human P2X(7) receptors expressed in HEK transfected cells with K(D) and B(max) value of 3.46+/-0.1 nM and 727+/-73 fmol/mg of protein, respectively. The high affinity and facile labeling makes it a promising radioligand for a further characterization of P2X(7) receptor subtype.

Arylsulfonates↗

PubMed2004

Synthesis and biological evaluation of novel N6-[4-(substituted)sulfonamidophenylcarbamoyl]adenosine-5'-uronamides as A3 adenosine receptor agonists.

A new series of 1-deoxy-1-[(6-(4-(substituted-aminosulfonyl)phenyl)amino)carbonylamino-9H-purin-9-yl]-N-ethyl-beta-D-ribofuranuronamides (83-102) have been synthesized and tested at the human A3 adenosine receptor subtype. All the derivatives described in this work displayed affinity versus this receptor in the nanomolar range and good selectivity versus A1 adenosine receptor subtype, confirming that the p-sulfonamido moiety positively affected the activity of the molecules. The best substituents at the sulfonamido nucleus were found to be small alkyl groups, like methyl, isopropyl, ethyl, or allyl moieties (compounds 96-100), whereas monosubstitution at the amino group led to a decrease in A3 affinity values. The selectivity versus A1 adenosine receptor subtype is increased when the amino group in the sulfonamido core is represented by a hydrogenated heterocyclic ring like piperidine, morpholine, or pyrroline. Bulky groups, like adamantane and alkyl chains with more than four carbon atoms, are detrimental for the affinity and the selectivity of the A3 adenosine receptor agonists described here.

Adenosine↗

PubMed2004

Cinnamoyl nitrogen mustard derivatives of pyrazole analogues of tallimustine modified at the amidino moiety: design, synthesis, molecular modeling and antitumor activity studies.

The design, synthesis and in vitro activities of a series of cinnamoyl nitrogen mustard pyrazole analogues of tallimustine 8-13, in which the amidino moiety has been replaced by moieties of different physico-chemical features are described, and the structure-activity relationships are discussed. In spite of the relevance of these modifications on the amidino moiety, these derivatives showed significant growth inhibitory activity against mouse leukemia L1210 cells. A selected series of compounds have been evaluated for their sequence selective alkylating properties and cytotoxicity against human K562 leukemia cells. Therefore, the presence of the amidino moiety, and in general of a basic moiety, is not an absolute requirement for biological activity. Our preliminary results indicated that the compounds of this series have a pattern of alkylation similar to that of tallimustine, but they seem to be less reactive overall in alkylating naked DNA.

Animals↗

PubMed2004

[3H]-MRE 2029-F20, a selective antagonist radioligand for the human A2B adenosine receptors.

MRE 2029-F20 [N-benzo[1,3]dioxol-5-yl-2-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]-acetamide] is a selective antagonist ligand of A2B adenosine receptors. For use as a radioligand, 1,3-diallyl-xanthine, the precursor of [3H]-MRE 2029-F20, was synthesized, and tritiated on the allyl groups. [3H]-MRE 2029-F20 bound to human A2B receptors expressed in CHO cells showed a KD value of 1.65+/-0.10 nM and Bmax value of 36+/-4 fmol/mg protein. [3H]-MRE2029-F20 represents a useful tool for the pharmacological characterization of human A2B adenosine receptor subtype.

Acetamides↗

PubMed2004

Design, synthesis, and biological evaluation of hybrid molecules containing alpha-methylene-gamma-butyrolactones and polypyrrole minor groove binders.

We have synthesized and evaluated a series of hybrids of polypyrrole minor groove binders structurally related to the natural antitumor agent distamycin A, and alpha-methylene-gamma-butyrolactones with methyl, phenyl, and 4-substituted phenyl groups at the lactone C(gamma) position, denoted 5-17, for in vitro cytotoxic activity against a variety of cancer cell lines. The apoptotic and cytotoxic activities against several tumor cell lines are reported and discussed in terms of their structural differences in relation to both the number of N-methylpyrrole rings and the type of the alkylating unit tethered to the oligopeptidic frame. It may be noted that in general, and especially for 11, 12, and 17, the cytotoxicity of the hybrids was much greater than that of the alpha-methylene-gamma-butyrolactone units 24a-g alone. Using the human leukemia cell line HL-60, we have tested the effects of a selected series of compounds on programmed cell death (apoptosis). The results clearly indicate that 11, 12, and 17, but not 9, are able to induce apoptosis as demonstrated from (i) identification of nuclear changes associated with apoptosis using fluorescence microscopy and (ii) by DNA laddering on agarose gel electrophoresis. Compound 12 was the most potent, especially after a short incubation period. It induced extensive hydrolysis of poly ADP-ribose polymerase (PARP), considered to be a hallmark of apoptosis, which plays a critical role in chromatin architecture and DNA metabolism.

4-Butyrolactone↗

PubMed2004

Cytotoxic alpha-halogenoacrylic derivatives of distamycin A and congeners.

The mechanism of action of many antitumor agents involves DNA damage, either by direct binding of the drug to DNA or to DNA-binding proteins. However, most of the DNA-interacting agents have only a limited degree of sequence specificity, which implies that they may hit all the cellular genes. DNA minor groove binders, among which the derivatives of distamycin A play an important role, could provide significant improvement in cancer management, increasing gene specificity, due to high selectivity of interaction with thymine-adenine (TA) rich sequences. We now report and discuss the synthesis, the in vitro and in vivo activities, and some mechanistic features of alpha-halogenoacrylamido derivatives of distamycin A. The final result of this work was the selection of brostallicin 17 (PNU-166196). Brostallicin, presently in phase II clinical trials, shows a broad spectrum of antitumor activity and an apoptotic effect higher than distamycin derivative tallimustine. An important in vitro toxicological feature of brostallicin is the very good ratio between myelotoxicity on human haematopoietic progenitor cells and cytotoxicity on tumor cells, in comparison with clinically tested DNA minor groove binders. A peculiarity of brostallicin is its in vitro reactivity in the DNA alkylation assays only in the presence of glutathione. Moreover brostallicin's antitumor activity, both in in vitro and in vivo tumor models, is higher in the presence of increased levels of glutathione/glutathione-S-tranferases. These findings contribute to the definition of brostallicin as a novel anticancer agent that differs from other minor groove binders and alkylating agents for both the profile of activity and the mechanism of action and to classify the alpha-bromoacrylamido derivatives of distamycin as a new class of cytotoxics. Moreover, due to its interaction with glutathione, brostallicin may have a role for the tailored treatment of tumors characterized by constitutive or therapy-induced overexpression of glutathione/glutathione-S-tranferase levels.

Animals↗

PubMed2004

Design, synthesis, and biological evaluation of new 8-heterocyclic xanthine derivatives as highly potent and selective human A2B adenosine receptor antagonists.

Here we report the synthesis of 8-heterocycle-substituted xanthines as potent and selective A(2B) adenosine receptor antagonists. The structure-activity relationships (SAR) of the xanthines synthesized in binding to recombinant human A(2B) adenosine receptors (ARs) in HEK-293 cells (HEK-A(2B)) and at other AR subtypes were explored. The synthesized compounds showed A(2B) adenosine receptor affinity in the nanomolar range and good levels of selectivity evaluated in radioligand binding assays at human (h) A(1), A(2A), A(2B), and A(3) ARs. We introduced several heterocycles, such as pyrazole, isoxazole, pyridine, and pyridazine, at the 8-position of the xanthine nucleus and we have also investigated different spacers (substituted acetamide, oxyacetamide, and urea moieties) on the heterocycle introduced. Various groups at the 3- and 4-positions of phenylacetamide moiety were studied. This study allowed us to identify the derivatives 2-(3,4-dimethoxyphenyl)-N-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yl]acetamide (29b, MRE2028F20) [K(i)(hA(2B)) = 38 nM, K(i)(hA(1),hA(2A),hA(3)) >1000 nM], N-benzo[1,3]dioxol-5-yl-2-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]acetamide (62b, MRE2029F20) [K(i)(hA(2B)) = 5.5 nM, K(i)(hA(1),hA(2A),hA(3)) > 1000 nM], and N-(3,4-dimethoxyphenyl)-2-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]acetamide (72b, MRE2030F20) [K(i)(hA(2B) = 12 nM, K(i)(hA(1),hA(2A), hA(3)) > 1000 nM], which showed high affinity at the A(2B) receptor subtype and very good selectivity vs the other ARs. Substitution of the acetamide with an urea moiety afforded bioisosteric xanthines with good affinity and selectivity comparable to the acetamide derivatives. Substitution at the para-position of a 4-benzyloxy group of the phenylacetamido chain enhanced affinity at the A(2B) receptor [compound 30b (K(i)(hA(2B)) = 13 nM) vs compound 21b (K(i)(hA(2B) = 56 nM)] but did not favor selectivity. The derivatives with higher affinity at human A(2B) AR proved to be antagonists, in the cyclic AMP assay, capable of inhibiting the stimulatory effect of NECA (100 nM) with IC(50) values in the nanomolar range, a trend similar to that observed in the binding assay (62b, IC(50) = 38 nM; 72b, IC(50) = 46 nM). In conclusion, the 8-pyrazolo-1,3-dipropyl-1H-purine-2,6-dione derivatives described herein represent a new family of selective antagonists for the adenosine A(2B) receptor.

Adenosine A1 Receptor Antagonists↗

PubMed2004

Binding of hybrid molecules containing pyrrolo [2,1-c][1,4]benzodiazepine (PBD) and oligopyrrole carriers to the human immunodeficiency type 1 virus TAR-RNA.

The binding properties of a set of four hybrids, prepared combining from one to four polypyrrole minor groove binders and pyrrolo [2,1-c][1,4]benzodiazepine (PBD), have been studied using as target molecule the HIV-1 TAR-RNA. We found that these hybrids bind to TAR-RNA and inhibit TAR/protein(s) interactions. The anti-proliferative activity of the hybrids has been tested in vitro on HL3T1 cells and compared to the anti-proliferative effects of the natural product distamycin A and PBD. The effects on HIV-1 LTR directed transcription were studied using the chloramphenicol-acetyltransferase gene reporter system, and structure-activity relationships are discussed. The results obtained demonstrate that the hybrids 22-25 exhibit different TAR-RNA binding activity with respect to both distamycin A and PBD. In addition, a direct relationship was found between number of pyrrole rings present in the hybrids 22-25 and anti-proliferative effects. It was found that increased length of the polypyrrole backbone leads to an increased in vitro anti-proliferative effect, i.e. the hybrid 25, containing the four pyrroles distamycin analogous, is more active than 22, 23 and 24 against cell proliferation. With respect to inhibition of HIV-1 LTR-driven transcription, it was found that the hybrids 23-25 containing two-four pyrroles are active. Therefore, when anti-proliferative effects are considered together with the inhibitory effects of HIV-1 LTR driven transcription, our results suggest that the hybrid 23 is the more interesting, since it exhibits low anti-proliferative activity and inhibits HIV-1 LTR driven transcription both in vitro and in ex vivo experiments.

Antiviral Agents↗

PubMed2004

Synthesis of nitro esters of prednisolone, new compounds combining pharmacological properties of both glucocorticoids and nitric oxide.

Glucocorticoids (GC) are widely used in therapy for their many pharmacological properties including antiinflammatory and immunosuppressive actions. However, their use over long periods is hampered by a number of severe side effects. Given the biological properties of nitric oxide (NO) and previous experience with nonsteroidal antiinflammatory agents, we synthesized new chemical entities combining both NO and GC properties. Here we report the synthesis of nitro esters of prednisolone obtained through the esterification, with different linkers, on the hydroxy group at C-21 position of the corticosteroid structure. The alkyl chain, as of the nitrooxy derivative (2), or aromatic linkers, as of o-, m-, and p-nitrooxymethylbenzoate derivatives (3-5), respectively, furnish stable compounds that release NO and inhibit the GC receptors in biological assays. To improve solubility we introduced a more water-soluble linker such as the nitrooxyalkylpiperidine or -piperazine group (6-9). Also these compounds retained properties of both NO and prednisolone. Compound 5 (NCX 1015) was selected for its better profile: enhanced antiinflammatory properties and reduced side effects compared with prednisolone. NCX 1015 is currently under preclinical development.

Animals↗

PubMed2004

DNA minor groove binders as potential antitumor and antimicrobial agents.

DNA minor groove binders constitute an important class of derivatives in anticancer therapy. Some of these compounds form noncovalent complexes with DNA (e.g., distamycin A, Hoechst 33258, and pentamidine) while others DNA-binding compounds (such as CC-1065) cause cleavages in the DNA backbone. In this article, we have reviewed the minor groove binders currently in preclinical evaluation in the last years. Diarylamidines such as DAPI, berenil, and pentamidine; bis-benzimidazoles such as Hoechst 33258; ecteinascidins, pyrrololo [2,1-c]-[1,4]-benzodiazepines (PBDs), CC-1065, and distamycins are the classes discussed in this review article. A special section has been dedicated to hybrid molecules resulted by the combination of two minor groove binders, especially for derivatives of naturally occurring antitumor agents, such as anthramycin or the alkylating unit of the antibiotic CC-1065, and distamycin frames.

Anti-Infective Agents↗

PubMed2004

Synthesis of 2-amino-3-heteroaroylthiophenes and evaluation of their activity as potential allosteric enhancers at the human A1 receptor.

2-Amino-3-benzoylthiophenes are allosteric enhancers of agonist binding to the adenosine A(1) receptor. New compounds bearing an heteroaroyl instead of the benzoyl moiety at the 3-position of the thiophene were synthesized. The phenyl ring was replaced with heterocycles that possess heteroatoms able to form hydrogen bonds (2-furanyl, 2-benzofuranyl, 2-pyridinyl in compounds 2-13) or with a thienyl moiety as isoster of the phenyl ring (2-thienyl, 3-thienyl and 5-halo-2-thienyl in compounds 14-29). The effect of several alkyl substituents at positions 4 and 5 of the thiophene ring to increase enhancer activity was determined. The ability of the new molecules to reduce the cAMP content in CHO cells expressing the human adenosine A(1) receptor was evaluated. Compounds 2-13 with hydrogen bond-forming heteroatoms did not show significant activity as allosteric enhancers. On the other hand, compounds 15-16 and 19-20 with an unsubstituted thienyl moiety as replacement for the phenyl ring were nearly as efficacious as PD 81,723, the prototypical A(1) allosteric enhancer. Alkyl substituents at positions 4 and 5 of the thiophene ring were tolerated while a substituted piperidine ring was not tolerated. We conclude that hydrogen bonds could not be formed in the domain of the receptor that accommodates the phenyl ring of 2-amino-3-benzoylthiophene derivatives, indicating that this domain is hydrophobic.

Allosteric Regulation↗

PubMed2004

Agonists and antagonists acting at P2X7 receptor.

The P2X(7) receptor is involved in several processes relevant to inflammation (cytokine release, NO generation, killing of intracellular pathogens, cytotoxicity), thus, it may be an appealing target for pharmacological intervention. The characterisation of native and recombinant P2X(7) receptor continues to be hindered by the lack of specific and subtype-selective agonists and antagonists. BzATP is currently the most potent agonist known at the endogenous and recombinant P2X(7) receptor A tyrosine derivative named KN-62 exhibits selective P2X(7) receptor-blocking properties. In this review article we have reported novel series of KN-62-related compounds of the general structure R(1)-Tyr(OR(2))-piperazinyl-R(3), in which three positions (R(1), R(2) and R(3)) were systematically varied. Two recent articles published by AstraZeneca have reported that novel series of cyclic imides and adamantane amides are potent P2X(7) receptor antagonists.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed2004

Distamycin A as stem of DNA minor groove alkylating agents.

Analogues of naturally occurring antitumor agents, such as distamycin A, which bind in the minor groove of DNA, represent a new class of anticancer compounds currently under investigation. Distamycin A has driven researcher's attention not only for their biological activity, but also for its non intercalative binding to the minor groove of double-stranded B-DNA, where it forms strong reversible complex preferentially at the nucleotide sequences consisting of 4-5 adjacent AT base pairs. The pyrrole-amide skeleton of distamycin A has been also used as DNA sequence selective vehicles for the delivery of alkylating functions to DNA targets, leading to a sharp increase of its cytotoxicity, in comparison to that, very weak, of distamycin itself. In the last few years, several hybrid compounds, in which known antitumor derivatives or simple active moieties of known antitumor agents have been tethered to distamycin frames, have been designed, synthesized and tested. Several efforts have been made to modify DNA sequence selectivity and stability of the distamycin and the structural modifications have been based on replacement of pyrrole by other heterocycles and/or benzoheterocycles obtaining a novel class of minor groove binding molecules called lexitropsins. The role of the amidino moiety, by means of the substitution with various groups, which includes ionizable, acid or basic, and non-ionizable groups, has been also studied. The synthesis of a hybrid deriving among the combination of the distamycin A and naturally occurring alkylating agent has been also reported. Several classes of distamycin derivatives that have been reported in the published literature have been described in this review article.

Alkylating Agents↗