Novel 8-heterocyclyl xanthine derivatives in drug development - an update

Naturally occurring methyl xanthines, especially caffeine and theophylline, have been widely investigated for their pharmacological properties as cognition enhancers, bronchodilator agents and mild diuretics. The xanthine core (3,7-dihydro-1H-purine-2,6-dione) has been largely manipulated in the search for selective ligands for different pharmacological targets, proving to be a versatile scaffold for the development of lead compounds in multiple therapeutic areas. The introduction of a heterocycle at the 8-position of some xanthine derivatives demonstrated to be a successful strategy for the identification of potent and selective A1 or A2B adenosine receptors antagonists as potential agents for the treatment of Alzheimer's disease and asthma, respectively. Interesting examples of 8-heterocyclyl-xanthines as dipeptidyl peptidase IV inhibitors and liver X receptor agonists have been claimed for their possible therapeutic use in the treatment of Type 2 diabetes and atherosclerosis.

Chemical synthesis of [(13)c]daidzein

Pharmacokinetic and metabolic studies of phytoestrogens of the isoflavone class have been hampered by the lack of suitable stable-isotope-labeled analogs. A method for preparation of a [(13)C]-labeled analog of daidzein is described. [2-(13)C]Daidzein was synthesized by reaction of [(13)C]diethoxydimethylaminomethane with 2,4-dihydroxybenzoin. The final product was purified to more than 99% by reverse-phase high-performance liquid chromatography and structural analysis confirmed by nuclear magnetic resonance spectroscopy and mass spectrometry. Because [2-(13)C]daidzein is analytically and metabolically stable, it is a suitable analog for use as an internal standard for quantifying daidzein in biological fluids using isotope dilution mass spectrometry. This nonradioactive tracer is also ideal for investigating the pharmacokinetics of daidzein in humans because it is biologically indistinguishable from the unlabeled form.

Transient receptor potential ankyrin receptor 1 is a novel target for pro-tussive agents

BACKGROUND AND PURPOSE

The transient receptor potential ankyrin receptor 1 (TRPA1) is a cation channel, co-expressed with the pro-tussive transient receptor potential vanilloid type 1 (TRPV1) channel in primary sensory neurons. TRPA1 is activated by a series of irritant exogenous and endogenous alpha,beta-unsaturated aldehydes which seem to play a role in airway diseases. We investigated whether TRPA1 agonists provoke cough in guinea pigs and whether TRPA1 antagonists inhibit this response.

EXPERIMENTAL APPROACH

Animals were placed in a Perspex box, and cough sounds were recorded and counted by observers unaware of the treatment used.

KEY RESULTS

Inhalation of two selective TRPA1 agonists, allyl isothiocyanate and cinnamaldehyde, dose-dependently caused cough in control guinea pigs, but not in those with airway sensory nerves desensitized by capsaicin. Coughs elicited by TRPA1 agonists were reduced by non-selective (camphor and gentamicin) and selective (HC-030031) TRPA1 antagonists, whereas they were unaffected by the TRPV1 antagonist, capsazepine. Acrolein and crotonaldehyde, two alpha,beta-unsaturated aldehydes recently identified as TRPA1 stimulants and contained in cigarette smoke, air pollution or produced endogenously by oxidative stress, caused a remarkable tussive effect, a response that was selectively inhibited by HC-030031. Part of the cough response induced by cigarette smoke inhalation was inhibited by HC-030031, suggesting the involvement of TRPA1.

CONCLUSIONS AND IMPLICATIONS

A novel pro-tussive pathway involves the TRPA1 channel, expressed by capsaicin-sensitive airway sensory nerves and is activated by a series of exogenous (cigarette smoke) and endogenous irritants. These results suggest TRPA1 may be a novel target for anti-tussive medicines.

Blockade of globus pallidus adenosine A(2A) receptors displays antiparkinsonian activity in 6-hydroxydopamine-lesioned rats treated with D(1) or D(2) dopamine receptor agonists

We have recently demonstrated how antagonism of adenosine A(2A) receptors within the globus pallidus (GP) ipsilateral to dopaminergic denervation potentiates contralateral rotational behavior induced by the dopamine precursor L-DOPA in 6-hydroxydopamine-lesioned hemiparkinsonian rats. To further characterize the influence of pallidal A(2A) receptor blockade on the motor stimulant effects elicited by dopamine receptor activation, hemiparkinsonian rats were infused with the water-soluble A(2A) antagonist SCH BT2 in the GP, alone or in combination with systemic administration of either SKF 38393 or quinpirole, to stimulate dopamine D(1) or D(2) receptors, respectively. SCH BT2 alone (5 mug/1 mul) neither altered motor behavior nor produced postural asymmetry. In contrast, the contralateral rotations elicited by SKF 38393 (1.5 mg/kg) as well as quinpirole (0.05 mg/kg) were potentiated by the concomitant intrapallidal infusion of SCH BT2. The results of this study demonstrate that blockade of pallidal A(2A) receptors exerts a facilitatory influence on the motor effects produced by the selective stimulation of either D(1) or D(2) dopamine receptors in hemiparkinsonian rats and suggest an involvement of GP in the antiparkinsonian activity of A(2A) receptor antagonists.

Dopamine and adenosine receptor interaction as basis for the treatment of Parkinson's disease

Preclinical evidence strongly indicate that adenosine A(2A) receptor antagonists represent a promising class of drugs for the treatment of motor deficits associated to Parkinson's disease. The effects of adenosine A(2A) receptor antagonists were here assessed in a rat model of parkinsonian tremor induced by cholinomimetic drugs by evaluating the counteraction of tremulous jaw movements. Systemic administration of the A(2A) antagonist SCH 58261 dose-dependently reduced the magnitude of perioral tremor induced by the acetylcholinesterase inhibitor tacrine (2.5 mg/kg). Furthermore, intrastriatal infusion of SCH BT2 (5 microg/microl), a water-soluble analogue of SCH 58261, antagonized tacrine-induced jaw movements with a maximal effect in the ventrolateral striatum. On the other hand, SCH 58261 (5 mg/kg) was ineffective in blocking tremulous jaw movements stimulated by the direct muscarinic agonist pilocarpine (1 mg/kg). Taken together, these results indicate that A(2A) antagonists reduce parkinsonian tremor stimulated in rats by tacrine and that the striatum is deeply involved in the observed effect. Moreover, the ineffectiveness of SCH 58261 in blocking pilocarpine-stimulated perioral tremor suggests that the antitremorigenic effects of A(2A) antagonists described here are not related to a direct action on muscarinic receptor. The prospective of providing additional antitremor benefits considerably enhances the therapeutic potential of A(2A) antagonists.

Involvement of globus pallidus in the antiparkinsonian effects of adenosine A(2A) receptor antagonists

An involvement of globus pallidus (GP) in the antiparkinsonian effects of A(2A) receptor antagonists has been proposed on the basis of the selective localization of A(2A) receptors on the striatopallidal pathway. In order to investigate this possibility, the present study evaluated rotational behavior in unilaterally 6-hydroxydopamine-lesioned rats following infusion of the water-soluble A(2A) receptor antagonist SCH BT2 into GP. SCH BT2 (5 microg/1 microl) altered neither motor behavior nor produced postural asymmetry by itself. However, when infused concomitantly with a parenteral subthreshold dose of l-DOPA (3 mg/kg i.p.) capable of inducing modest contralateral rotational behavior (34.7 +/- 20.7/1 h), SCH BT2 significantly potentiated the number of contraversive rotations (167.4 +/- 16.3/1 h). These results suggest that A(2A) receptors located in the globus pallidus may be involved in the antiparkinsonian effects of A(2A) antagonists.

Molecular modeling and molecular dynamics simulation of the human A2B adenosine receptor. The study of the possible binding modes of the A2B receptor antagonists

A molecular model of the human A(2B) adenosine receptor containing seven transmembrane alpha helices connected by three intracellular and three extracellular hydrophilic loops had been constructed. A molecular docking of seven structurally diverse xanthine antagonists of the A(2B) receptor was performed, and the differences in their binding modes were investigated. The 1 ns molecular dynamics (MD) simulations of several obtained ligand-receptor complexes inserted into the phospholipid bilayer were carried out. The conformational changes of the A(2B) receptor occurring during MD simulations were explored, and the stable binding modes of the studied antagonists were determined. According to the models presented in this work, the involvement of the His251, Asn282, Ser92, Thr89, and some aromatic residues in ligand recognition was determined. The obtained binding modes of the A(2B) antagonists demonstrate good agreement with the site-directed mutagenesis data.

Regioselective One-Pot Synthesis of 9-Alkyl-6-chloropyrido[3,2-e][1,2,4]triazolo[4,3-a]pyrazines. Reactivity of Aliphatic and Aromatic Hydrazides

[reaction: see text] The one-pot synthesis of new 9-alkyl-6-chloropyrido[3,2-e][1,2,4]triazolo[4,3-a]pyrazines has been achieved. Hydrazides regioselectively reacted as nucleophiles with the 3-chloro substituent of 2,3-dichloropyrido[2,3-b]pyrazine. An intramolecular cyclization afforded the tricycle nonxanthine adenosine receptor antagonists.

Blockade of adenosine A2A receptors antagonizes parkinsonian tremor in the rat tacrine model by an action on specific striatal regions

Acute administration of the acetylcholinesterase inhibitor tacrine to rats induces tremulous jaw movements which can be used as a valuable model of parkinsonian tremor. In the present study, the number of tremor episodes and jaw movements were evaluated to assess the effects of the selective A2A antagonists SCH 58261 and SCH BT2 on tremorgenesis. SCH 58261 dose-dependently, and maximally at 5 mg/kg, reduced the number of both tremor episodes (-35%) and jaw movements (-50%), induced in rats by tacrine (2.5 mg/kg ip). Since adenosine A2A receptors are largely expressed throughout the striatum, chronic cannulae were implanted in the rat dorsomedial (DMS) and ventrolateral striatum (VLS) to investigate whether A2A antagonists could act at this level. Infusion of SCH BT2 (5 microg/microl), a water-soluble analogue of SCH 58261, in VLS antagonized both tremor episodes (-68%) and jaw movements (-76%) elicited by tacrine (2.5 mg/kg ip), whereas SCH BT2 infusion in DMS was less effective in blocking jaw movements (-50%) and did not significantly affect the number of tremor episodes. Taken together, the results of this study indicate that A2A antagonists effectively reduce the magnitude of tremulous jaw movements induced in rats by acute tacrine, mainly by an action in VLS and suggest that A2A antagonists might be used as specific agents against parkinsonian tremor.

Blockade of A2A receptors plus l-DOPA after nigrostriatal lesion results in GAD67 mRNA changes different from l-DOPA alone in the rat globus pallidus and substantia nigra reticulata

Studies in animal models of Parkinson's disease (PD) suggest the potential utility of adenosine A(2A) antagonists in the treatment of this disease. In the present study, unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats received chronic intermittent treatment with the adenosine A(2A) antagonist SCH58261 (5 mg/kg) plus l-DOPA (3 mg/kg) or l-DOPA (6 mg/kg) alone, at doses producing the same intensity of contralateral turning on first administration. Three days after discontinuation of treatments, GABA synthesizing enzyme glutamic acid decarboxylase (GAD67) mRNA was evaluated at cellular level in the globus pallidus (GP) and substantia nigra pars reticulata (SNr) by in situ hybridization. 6-OHDA lesion significantly increased GAD67 mRNA levels in both the GP and SNr ipsilateral to the lesion. Chronic l-DOPA (6 mg/kg), in contrast to SCH58261 plus l-DOPA (3 mg/kg), produced a sensitized contralateral turning indicative of dyskinetic potential and further increased GAD67 mRNA in the GP. In the SNr, a significant decrease in GAD67 mRNA was observed after either treatments. However, while l-DOPA (6 mg/kg) decreased SNr GAD67 mRNA below the intact side, SCH58261 plus l-DOPA (3 mg/kg) brought GAD67 mRNA to the same level of the intact SNr. l-DOPA (3 mg/kg) or SCH58261 (5 mg/kg) alone failed to modify GAD67 mRNA. Results suggest that an increase in GAD67 mRNA in GP and a decrease in SNr might underlie dyskinetic movements induced by chronic l-DOPA. In contrast, the lack of GAD67 mRNA changes in the GP and a less marked inhibition of SNr might correlate with the absence of dyskinetic potential observed after SCH58261 plus l-DOPA.

Selective adenosine A2A receptor antagonists

In the early 1990s it became clear that the A2A adenosine receptor had characteristics that made it distinct from the other A1, A2B and A3 adenosine receptors. Great progress has been made with the discovery of selective A2A receptor antagonists. A variety of synthetic substitutions on the xanthine moiety led the chemists of Kyowa-Hakko to discover that introduction of the styryl group in the 8 position of xanthines was critical in achieving compounds endowed with selective A2A receptor antagonistic properties. One compound, KW 6002, (E)1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methylxanthine, is currently being developed for treatment of Parkinson's disease. A number of non-xanthine heterocycles have also been synthesized starting from the non-selective adenosine antagonist CGS 15943, a triazoloquinazoline. Thus, replacement of the phenyl ring of CGS 15943 with a heterocyclic ring such as pyrazole or imidazole, led to a series of interesting compounds whose prototype, SCH 58261, 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine, has become a reference A2A receptor antagonist. Modification of N7 substituents has progressed to optimize A2A receptor selectivity and pharmacokinetic characteristics. A related class of compounds having a bicyclic instead of the tricyclic ring structure is also of interest. The prototype of these triazintriazolo derivatives, ZM 241385, is a potent A2A receptor antagonist; however, it also shows interactions with A2B receptors. The relevance of the A2A receptors in specific disease states, especially in the central nervous system, makes this class of adenosine receptor blockers of interest for treatment of neurodegenerative disorders such as Parkinson's disease.

Fluorosulfonyl- and bis-(beta-chloroethyl)amino-phenylamino functionalized pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine derivatives: irreversible antagonists at the human A3 adenosine receptor and molecular modeling studies

A series of pyrazolotriazolopyrimidines was previously reported to be highly potent and selective human A(3) adenosine receptor antagonists (Baraldi et al. J. Med. Chem. 2000, 43, 4768-4780). A derivative having a methyl group at the N(8) pyrazole combined with a 4-methoxyphenylcarbamoyl moiety at N(5) position, displayed a K(i) value at the hA(3) receptor of 0.2 nM. We now describe chemically reactive derivatives which act as irreversible inhibitors of this receptor. Electrophilic groups, specifically sulfonyl fluoride and nitrogen mustard (bis-(beta-chloroethyl)amino) moieties, have been incorporated at the 4-position of the aryl urea group. Membranes containing the recombinant hA(3) receptor were preincubated with the compounds and washed exhaustively. The loss of ability to bind radioligand following this treatment indicated irreversible binding. The most potent compound in irreversibly binding to the receptor was 14, which contained a sulfonyl fluoride moiety and a propyl group at the N(8) pyrazole nitrogen. The bis-(beta-chloroethyl)amino derivatives displayed a much smaller degree of irreversible binding than the sulfonyl fluoride derivatives. A computer-generated model of the human A(3) receptor was built and analyzed to help interpret these results. The model of the A(3) transmembrane region was derived using primary sequence comparison, secondary structure predictions, and three-dimensional homology building, using the recently published crystal structure of rhodopsin as a template. According to our model, sulfonyl fluoride derivatives could dock within the hypothetical TM binding domain, adopting two different energetically favorable conformations. We have identified two amino acids, Ser247 and Cys251, both in TM6, as potential nucleophilic partners of the irreversible binding to the receptor.

Design, synthesis, DNA binding, and biological evaluation of water-soluble hybrid molecules containing two pyrazole analogues of the alkylating cyclopropylpyrroloindole (CPI) subunit of the antitumor agent CC-1065 and polypyrrole minor groove binders

We have synthesized and evaluated a series of hybrids, denoted 22--27, for in vitro cytotoxic activity against a variety of cancer cell lines. These hybrids represent a molecular combination of polypyrrole minor groove binders structurally related to the natural antitumor agent distamycin A and two pyrazole analogues of the left-hand segment called cyclopropylpyrroloindole (CPI) of the potent antitumor antibiotic (+)-CC-1065. These novel water-soluble hybrids have been designed to enhance the minor groove binding ability of alkylating units 20 and 21, which should increase their clinical appeal by overcoming the administration problems of (+)-CC-1065 derivatives. The DNA alkylating 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-methyl pyrrole rings and the type of the alkylating unit tethered to the oligopeptidic frame. It may be noted that, in general, and especially for 22--24, the cytotoxicity of the hybrids was much greater than that of the alkylating units alone. In only one case, compound 27, did the hybrid have cytotoxic activity comparable to that of the alkylating unit alone against FM3A/0 cells. The broadest spectrum of activity and greatest potency was shown by the hybrid 24, in which the alkylating unit 20 and the deformyl distamycin A are tethered by 1-methyl 2,5-dicarbonyl pyrazole, with IC(50) values for the different tumor cell lines ranging from 7 to 71 nM. For compounds 22--24, the increase of the length of the pseudopeptidic moiety from one to three N-methylpyrrole residues led to an increased cytotoxicity. Among the hybrids tested for their inhibitory effects on the proliferation of murine L1210 leukemia cell line, compound 24 proved to be the most active (IC(50) = 7.4 nM), and in the sequencing gel experiments, it showed the strongest and most highly sequence-specific DNA alkylation activity. For compounds 22-24, the sequence specificity of DNA alkylation appears to be affected by the modification of the number of pyrrole rings, and the correlation between cytotoxicity and alkylation pattern suggests that 24 exerts its cytotoxicity through DNA sequence-specific alkylation of the third adenine located in the sequence 5'-ACAAAAATCG-3'. The two other hybrids 22 and 23 were slightly less active for tumor cell proliferation, with IC(50) values of 58 and 19 nM, respectively. With only one exception, none of the compounds was endowed with antiviral activity at subtoxic concentrations. Compound 24 inhibited the effect of vaccinia virus at a concentration that was significantly lower than its minimum cytotoxic concentration for the E(6)SM host cells. These compounds gave distinct patterns of alkylation in AT-rich sequences, indicating that minor structural changes produced marked alterations in sequence selectivity.

Design, synthesis and enzymatic activity of highly selective human mitochondrial thymidine kinase inhibitors

Highly selective arabinofuranosyl nucleosides, which inhibit the mitochondrial thymidine kinase (TK-2) without affecting the closely related herpes simplex virus type 1 thymidine kinase (HSV-1 TK), varicella-zoster virus thymidine kinase (VZV-TK), cytosolic thymidine kinase (TK-1) or the multifunctional Drosophila melanogaster deoxyribonucleoside kinase (Dm-dNK), have been obtained. SAR studies indicate a close relation between the length of the substituent at the 2' position of the arabinofuranosyl moiety and the inhibitory activity.

Pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine derivatives as highly potent and selective human A(3) adenosine receptor antagonists: influence of the chain at the N(8) pyrazole nitrogen

An enlarged series of pyrazolotriazolopyrimidines previously reported, in preliminary form (Baraldi et al. J. Med. Chem. 1999, 42, 4473-4478), as highly potent and selective human A(3) adenosine receptor antagonists is described. The synthesized compounds showed A(3) adenosine receptor affinity in the sub-nanomolar range and high levels of selectivity evaluated in radioligand binding assays at human A(1), A(2A), A(2B), and A(3) adenosine receptors. In particular, the effect of the chain at the N(8) pyrazole nitrogen was analyzed. This study allowed us to identify the derivative with the methyl group at the N(8) pyrazole combined with the 4-methoxyphenylcarbamoyl moiety at the N(5) position as the compound with the best binding profile in terms of both affinity and selectivity (hA(3) = 0.2 nM, hA(1)/hA(3) = 5485, hA(2A)/hA(3) = 6950, hA(2B)/hA(3) = 1305). All the compounds proved to be full antagonists in a specific functional model where the inhibition of cAMP generation by IB-MECA was measured in membranes of CHO cells stably transfected with the human A(3) receptor. The new compounds are among the most potent and selective A(3) antagonists so far described. The derivatives with higher affinity at human A(3) adenosine receptors proved to be antagonists, in the cAMP assay, capable of inhibiting the effect of IB-MECA with IC(50) values in the nanomolar range, with a trend strictly similar to that observed in the binding assay. Also a molecular modeling study was carried out, with the aim to identify possible pharmacophore maps. In fact, a sterically controlled structure-activity relationship was found for the N(8) pyrazole substituted derivatives, showing a correlation between the calculated molecular volume of pyrazolo[4,3-e]1,2, 4-triazolo[1,5-c]pyrimidine derivatives and their experimental K(i) values.

Synthesis and biological effects of a new series of 2-amino-3-benzoylthiophenes as allosteric enhancers of A1-adenosine receptor

New derivatives of PD 81,723, an allosteric enhancer of agonist binding to the A1-adenosine receptor, have been synthesized and evaluated in an intact cell assay. Compounds 3a, 3o and 3p appeared to be more potent than PD 81,723 and at a concentration of 0.1 microM caused significant reductions of cAMP content of CHO cells expressing the human A1-adenosine receptor. Compounds 4e and 4o appeared to be allosteric enhancers at a low concentration and antagonists at a higher concentration, whereas compounds 3c, 3g, 3s and 4l appeared to be weak antagonists that are also allosteric enhancers at the higher concentration of 10 microM.

[2,1-c][1,4]benzodiazepine (PBD)-distamycin hybrid inhibits DNA binding to transcription factor Sp1

We designed and synthesized the hybrid 6, prepared combining the minor groove binders distamycin A and pyrrolo [2,1-c][1,4] benzodiazepine (PBD) 4, related to the natural occurring anthramycin (2) and DC-81 (3). In this paper, the effects of the compound 6 on molecular interactions between DNA and transcription factor Sp1 were studied. The results obtained demonstrate that PBD-distamycin hybrid is a powerful inhibitor of Sp1/DNA interactions.

Synthesis and antitumor activity of new benzoheterocyclic derivatives of distamycin A

The design, synthesis, and in vivo and in vitro antileukemic activity of a novel series of compounds (13-22 and 34), in which different benzoheterocyclic rings, bearing a nitrogen mustard or a benzoyl nitrogen mustard or an alpha-bromoacryloyl group as alkylating moieties, are tethered to a distamycin frame, are reported, and structure-activity relationships are discussed. The new derivatives were prepared by coupling nitrogen mustard-substituted, benzoyl nitrogen mustard-substituted, or alpha-bromoacryloyl-substituted benzoheterocyclic carboxylic acids 23-32 with desformyldistamycin (33) or in one case with its two-pyrrole analogue 35. With very few exceptions, the activities of compounds bearing the same alkylating moiety are slightly affected by the kind of the heteroatom present on the benzoheterocyclic ring. All novel compounds, with one exception, showed in vitro activity against L1210 murine leukemia cell line comparable to or better than that of tallimustine. The compounds in which the nitrogen mustard and the alpha-bromoacryloyl moieties are directly linked to benzoheterocyclic ring showed potent cytotoxic activities (IC(50) ranging from 2 to 14 nM), while benzoyl nitrogen mustard derivatives of benzoheterocycles showed reduced cytotoxic activities, and one compound (16) of this cluster was the sole derivative devoid of significant activity. Compound 18, a 5-nitrogen mustard N-methylindole derivative of distamycin, showed the best antileukemic activity in vivo, with a very long survival time (%T/C = 457), significantly increased in comparison to tallimustine (%T/C = 133), and was selected for further extensive evaluation. Arrested polymerase chain reaction and direct DNA fragmentation assays were performed for compound 18 and the structurally related compounds 13-17 and 19. The results obtained have shown that both alkylating groups and oligopeptide frames play a crucial role in the sequence selectivity of these compounds.

Synthesis of hybrid distamycin-cysteine labeled with 99mTc: a model for a novel class of cancer imaging agents

The synthesis of a hybrid constituted by distamycin A and cysteine labeled with the gamma-emitting radionuclide 99mTc to afford the conjugate complex 5 is reported. This new radiopharmaceutical is of potential interest as tumor imaging agent in diagnostic nuclear medicine. The preparation of the hybrid distamycin A-cysteine 4 has been achieved by coupling deformyldistamycin A and Boc-Dmt-OH. Compound 4 was then successfully labeled with 99mTc by reaction with the novel, high-electrophilic, metal-containing fragment [99mTc(N)(PP)]2+ (PP = diphosphine ligand) yielding the 1:1 complex 5.

[(3)H]MRE 3008F20: a novel antagonist radioligand for the pharmacological and biochemical characterization of human A(3) adenosine receptors

The lack of a radiolabeled selective A(3) adenosine receptor antagonist is a major drawback for an adequate characterization of this receptor subtype. This paper describes the pharmacological and biochemical characterization of the tritiated form of a new potent A(3) adenosine receptor antagonist, the pyrazolo triazolo pyrimidine derivative [(3)H]5N-(4-methoxyphenylcarbamoyl)amino-8-propyl-2-(2-furyl )pyrazolo [4,3-e] -1,2,4- triazolo[1,5-c]pyrimidine ([(3)H]MRE 3008F20). [(3)H]MRE 3008F20 bound specifically to the human adenosine A(3) receptor expressed in CHO cells (hA(3)CHO), and saturation analysis revealed a single high affinity binding site, K(D) = 0.80 +/- 0.06 nM, with a B(max) = 300 +/- 33 fmol/mg protein. This new ligand displayed high selectivity (1294-, 165-, and 2471-fold) in binding assay to human A(3) versus A(1), A(2A), and A(2B) receptors, respectively, and binds to the rat A(3) receptors with a K(i) > 10 microM. The pharmacological profile of [(3)H]MRE 3008F20 binding to hA(3)CHO cells was evaluated using known adenosine receptor agonists and antagonists with a rank order of potency consistent with that typically found for interactions with the A(3) adenosine receptors. In the adenylyl cyclase assay the same compounds exhibited a rank order of potency identical with that observed in binding experiments. Thermodynamic data indicated that [(3)H]MRE 3008F20 binding to hA(3)CHO is entropy- and enthalpy-driven in agreement with the typical behavior of other adenosine antagonists to A(1) and A(2A) receptors. These results show that [(3)H]MRE 3008F20 is the first antagonist radioligand with high affinity and selectivity for the human A(3) adenosine receptor and may be used to investigate the physiopathological role of A(3) adenosine receptors.

Synthesis of conformationally constrained analogues of KN62, a potent antagonist of the P2X7-receptor

Conformationally constrained analogues of KN62 containing 1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid with S configuration in position 3 were synthesized and their antagonist activities were tested on human macrophage cells. While KN62 is a potent antagonist of the P2X7 receptor, these analogues were inactive as antagonists and only one compound showed appreciable activity as P2X7 antagonist, which was 30 times weaker than that reported for KN62.

Pyrazole related nucleosides 5. Synthesis and biological activity of 2'-deoxy-2',3'-dideoxy- and acyclo-analogues of 4-iodo-1-beta-D-ribofuranosyl-3-carboxymethyl pyrazole (IPCAR)

Continuing our studies on the structure-activity relationships (SAR) of 4-iodo-1-beta-D-ribofuranosyl-3-carboxymethyl pyrazole (IPCAR), the ribofuranosyl moiety has been substituted with acyclic chains, namely 1-[(2-hydroxyethoxy)methyl]- and 1-[(1,3-dihydroxy-2-propoxy)methyl]-pyrazole derivatives (4, 5 and 8, 9 respectively), with the 2'-deoxy-beta-D-ribofuranosyl group (12 and 13) and finally with the 2',3'-dideoxy-D-glycero-pentofuranosyl-moiety (16 and 17). None of the new compounds display any interesting biological activity.

DNA sequence-recognizing properties of minor groove alkylating agents. Effects of the replacement of N-methylpyrrole by an N-methylimidazole on tallimustine and its own homologue

The linkage of an heterocycle, like N-methylimidazole, to minor DNA groove binders containing two or three pyrroles lead to a new class of oligopeptides with reduced antitumor activity both in vitro and in vivo if compared to tallimustine (CAS 115308-98-0) and its tetrapyrrole homologue 9. In the present paper is reported the correlation between the cytoxicity of tallimustine and its derivatives 9-11 with their ability to inhibit polymerase chain reaction (PCR) amplification of oestrogen receptor and Ha-ras gene sequences, containing A + T rich and G + C rich regions, respectively. Tallimustine and its tetrapyrrole homologue 9 were found to have higher sequence selectivity for the human oestrogen receptor (ER) gene with respect to the relative imidazole-containing analogues.

A(3) adenosine receptor ligands: history and perspectives

Adenosine regulates many physiological functions through specific cell membrane receptors. On the basis of pharmacological studies and molecular cloning, four different adenosine receptors have been identified and classified as A(1), A(2A), A(2B), and A(3). These adenosine receptors are members of the G-protein-coupled receptor family. While adenosine A(1) and A(2A) receptor subtypes have been pharmacologically characterized through the use of selective ligands, the A(3) adenosine receptor subtype is presently under study in order to better understand its physio-pathological functions. Activation of adenosine A(3) receptors has been shown to stimulate phospholipase C and D and to inhibit adenylate cyclase. Activation of A(3) adenosine receptors also causes the release of inflammatory mediators such as histamine from mast cells. These mediators are responsible for processes such as inflammation and hypotension. It has also been suggested that the A(3) receptor plays an important role in brain ischemia, immunosuppression, and bronchospasm in several animal models. Based on these results, highly selective A(3) adenosine receptor agonists and/or antagonists have been indicated as potential drugs for the treatment of asthma and inflammation, while highly selective agonists have been shown to possess cardioprotective effects. The updated material related to this field of research has been rationalized and arranged in order to offer an overview of the topic.

Synthesis and preliminary biological evaluation of [3H]-MRE 3008-F20: the first high affinity radioligand antagonist for the human A3 adenosine receptors

The synthesis and the preliminary biological evaluation of the first high affinity radioligand antagonist for the human A3 adenosine receptor, named [3H]-MRE 3008-F20 are reported. [3H]-MRE 3008-20 bound human A3 receptors expressed in CHO cells with K(D) and Bmax value of 0.82 +/- 0.08 nM and 297 +/- 28 fmol/mg of protein, respectively. [3H]-MRE 3008-F20 represents a useful tool for a further characterization of A3 adenosine receptor subtype.

Synthesis, in vitro antiproliferative activity, and DNA-binding properties of hybrid molecules containing pyrrolo[2,1-c][1, 4]benzodiazepine and minor-groove-binding oligopyrrole carriers

The synthesis, biological activity, and DNA-binding properties of a series of four hybrids prepared by combining polypyrrole minor groove binders and pyrrolo[2,1-c][1,4]benzodiazepine (PBD) 13, related to the naturally occurring anthramycin (3) and DC-81 (4), have been described, and structure-activity relationships have been discussed. These hybrids 22-25 contain from one to four pyrrole units, respectively. To investigate sequence selectivity and stability of drug/DNA complexes, DNase I footprinting and arrested polymerase chain reaction (PCR) were performed on human c-myc oncogene, estrogen receptor gene, and human immunodeficiency virus type 1 long terminal repeat (HIV-1 LTR) gene sequences. The antiproliferative activity of the hybrids has been tested in vitro on human myeloid leukemia K562 and T-lymphoid Jurkat cell lines and compared to antiproliferative effects of the natural product distamycin A 1, its tetrapyrrole homologue 17, DC 81 (4), and the PBD methyl ester 12. The results obtained demonstrate that the hybrids 22-25 exhibit different DNA-binding activity with respect to both distamycin A 1 and PBD 12. In addition, a direct relationship was found between number of pyrrole rings present in the hybrids 22-25 and stability of drug/DNA complexes. With respect to antiproliferative effects, it was found that the increase in the length of the polypyrrole backbone leads to an increase of in vitro antiproliferative effects, i.e., the hybrid 25 containing the four pyrroles is more active than 22, 23, and 24 both against K562 and Jurkat cell lines.

1H-pyrazolo[2,3-d][1,2,4]triazine-3,7-diones as a new class of human leukocyte elastase inhibitors

A novel series of 1H-2-phenyl-substituted-pyrazolo[2,3-d][1,2,4]triazine-3,7-diones (3a-g) as potential inhibitors of Human Leukocyte Elastase (HLE) are reported, the acyl-pyrazole being probably involved in the inhibition mechanism of the serino-protease enzymes. The most potent inhibitor both in vivo and in vitro was 2-o-methoxyphenyl-5-methyl-6-nitro-pyrazolo[2,3-d][1,2,4]triazine-3,7-di one (3e), which significantly suppressed the HLE-induced pulmonary injury in rats when administered orally (100 mg/kg, 3 h prior to HLE administration.

Resolution of a CPzI precursor, synthesis and biological evaluation of (+) and (-)-N-Boc-CPzI: a further validation of the relationship between chemical solvolytic stability and cytotoxicity

The chemical resolution, using N-tosyl-L-proline as a chiral auxiliary, of a racemate of the pyrazole analog (+/-)-N-Boc-CPzI of the left hand segment (CPI) of the antitumor agent CC-1065, and the cytotoxic evaluation of both enantiomers are described. The reported results further validate the direct relationship between chemical solvolytic stability of the cyclopropane ring and cytotoxicity proposed by Boger and coworkers.

5'-Phosphoramidates and 5'-diphosphates of 2'-O-allyl-beta-D-arabinofuranosyluracil, -cytosine, and -adenine: inhibition of ribonucleotide reductase

Continuing our studies on ribonucleotide reductase (RNR) mechanism-based inhibitors, we have now prepared the diphosphates (DP) of 2'-O-allyl-1-beta-D-arabinofuranosyl-uracil and -cytosine and 2'-O-allyl-9-beta-D-arabinofuranosyl-adenine and evaluated their inhibitory activity against recombinant murine RNR. 2'-O-Allyl-araUDP proved to be inhibitory to RNR at an IC(50) of 100 microM, whereas 2'-O-allyl-araCDP was only marginally active (IC(50) 1 mM) and 2'-O-allyl-araADP was completely inactive. The susceptibility of the parent nucleosides to phosphorylation by thymidine kinase and 2'-deoxycytidine kinase was also investigated, and all nucleosides proved to be poor substrates for the above-cited kinases. Moreover, prodrugs of 2'-O-allyl-araU and -araC monophosphates, namely 2'-O-allyl-5'-(phenylethoxy-L-alanyl phosphate)-araU and -araC, were prepared and tested against tumor cell proliferation but proved to be inactive. A molecular modeling study has been conducted in order to explain our results. The data confirm that for both the natural and analogue nucleoside diphosphates, the principal determinant interaction with the active site of RNR is with the diphosphate group, which forms strong hydrogen bonds with Glu623, Thr624, Ser625, and Thr209. Our findings indicate that the poor phosphorylation may represent an explanation for the lack of marked in vitro cytostatic activity of the test compounds.

Effect of A-ring modifications on the DNA-binding behavior and cytotoxicity of pyrrolo[2,1-c][1,4]benzodiazepines

Several A-ring-modified analogues of the DNA-binding antitumor agent DC-81 (5) have been synthesized in order to study structure-reactivity/cytotoxicity relationships. For two molecules (23 and 30) the modifications required the addition of a fourth ring to give the novel dioxolo[4,5-h]- and dioxano[5,6-h]pyrrolo[2,1-c][1, 4]benzodiazepin-11-one (PBD) ring systems, respectively. Another three analogues (34, 38, and 48) have the native benzenoid A-ring replaced with pyridine, diazine, or pyrimidine rings to give the novel pyrrolo[2,1-c][1,4]pyridodiazepine, pyrrolo[2,1-c][1, 4]diazinodiazepine, and pyrrolo[2,1-c][1,4]pyrimidinodiazepine systems, respectively. The other new analogues (16a,b) have extended chains at the C8-position of the DC-81 structure. During the synthesis of these compounds, a novel tin-mediated regiospecific cleavage reaction of the dioxole intermediate 18 was discovered, leading to the previously unknown iso-DC-81 (20). In addition, an unusual simultaneous nitration-oxidation reaction of 4-(3-hydroxypropoxy)-3-methoxybenzoic acid (8) was found to produce 3-(4-carboxy-2-methoxy-5-nitrophenoxy)propanoic acid (9), a key intermediate, in high yield. In general, the results of cytotoxicity and DNA-binding studies indicated that none of the changes made to the A-ring of the PBD system significantly improved either binding affinity or cytotoxicity in comparison to DC-81. This result suggests that the superior potency of natural products such as anthramycin (1), tomaymycin (2), and sibiromycin (3) is due entirely to differences in C-ring structure, and in particular exo or endo unsaturation at the C2-position and C2-substituents containing unsaturation. This study also provided information regarding the influence of A-ring substitution pattern on the relative stability of the interconvertible N10-C11 carbinolamine, carbinolamine methyl ether, and imine forms of PBDs.

Synthesis, cytostatic activity and inhibition of ribonucleotide reductase by 5'-phosphoramidates and 5'-diphosphates, of 2'-O-allyl-arabinofuranosyl nucleosides

The diphosphates of a series of 2'-O-allyl-1-beta-D-arabinofuranosyl derivatives, previously obtained by us, have been prepared and tested for their inhibitory activity in an in vitro assay using R1 and R2 subunits of the purified recombinant mouse ribonucleotide reductase (RNR). 2'-O-Allyl-araU diphosphate proved to be inhibitory, with an IC50 of 100 microM. The 5'-phosphoramidate pronucleotide of 2'-O-allyl-araU was also prepared and tested for inhibition of tumor cell proliferation.

Novel benzoyl nitrogen mustard derivatives of pyrazole analogues of distamycin A: synthesis and antileukemic activity

The design and synthesis of novel benzoic acid mustard (BAM) derivatives of distamycin A bearing one or more pyrazole rings replacing the pyrrole rings of the latter are described. In vitro and in vivo activities against L1210 leukemia are reported and discussed. Some of these compounds show an activity profile comparable to tallimustine 1. All the compounds bearing the pyrazole ring close to the BAM moiety show reduced cytotoxicity in comparison to derivatives characterized by the BAM linked to a pyrrole: the same effect has not been observed when occurring at the amidine terminus of the oligopeptidic frame.

PNU 157977: a new potent antitumour agent exhibiting low in vivo toxicity in mice injected with L1210 leukaemia cells

The design, synthesis, in vitro and in vivo activity against L1210 murine leukaemia of the dibromo nitrogen mustard derivative of 2, called PNU 157977, is described and the structure-activity relationship discussed. This dibromo derivative is almost two orders of magnitude more cytotoxic than the dichloro counterpart having the same oligopeptidic chain (IC50 2.7 ng/ml versus 225 ng/ml), and it showed in vivo an increased survival time which is 5- and 3-fold longer than that of tallimustine and 2 (and T/C 750 versus 133 and 213) respectively. Moreover PNU 157977 shows activity against the M5076 solid tumour markedly inferior to that of the closely analogous 2. Footprinting experiments conducted using the oestrogen receptor PCR probe as the footprinting target molecule show that PNU 157977 possesses a different sequence-specific alkylation and greater cleavage activity than either 2 or tallimustine.

DNA minor-groove binders: results and design of new antitumor agents

DNA minor-groove binding drugs have been extensively studied in the last years in order to influence the regulation of gene expression in neoplastic disorders by means of specific interactions with DNA bases. Pyrrolo[2,1-c][1,4]benzodiazepines (PBDs), CC-1065 and distamycins are three classes of minor-groove alkylating agents which showed interesting cytotoxicity profiles, but they cannot be used in humans for various toxicity problems. For this reason many groups applied heterocyclic substitutions extensively, in order to either modify the reactivity profile or introduce extra interactions within the minor groove, thus changing the binding site or modulating the binding sequence.

Synthesis of novel C7-aryl substituted pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) via pro-N10-Troc protection and Suzuki coupling

Novel C7-aryl pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) have been synthesized via Suzuki coupling between a 7-Iodo N10-Troc-protected PBD carbinolamine and commercially available boronic acids.

Design, synthesis and biological activity of a pyrrolo [2,1-c][1,4]benzodiazepine (PBD)-distamycin hybrid

We report the synthesis of a new hybrid 13 which is a combination of the naturally occurring antitumor agent distamycin A 1 and the pyrrolo[2,1-c][1,4]benzodiazepine 11, related to the naturally occurring anthramycin 2. The antitumor activity of the hybrid 13 was tested in vitro and compared to the natural product distamycin 1 and the PBD 11.

Binding affinity of adenosine receptor agonists and antagonists at human cloned A3 adenosine receptors

The A3 adenosine receptor is one of the four adenosine receptors which have thus far been identified. Cloning of the A3 receptor from animal species such as rat, sheep and human has shown that there are interspecies differences in its peripheral distribution, and binding affinity for various adenosine receptor ligands. The adenosine derivative, 4-aminobenzyl-5'-N-methylcarboxamidoadenosine (AB-MECA), is a potent A3 receptor agonist which is used as a reference drug. In this report we have characterized the binding of selected adenosine receptor agonists and antagonists to HEK 293 cells transfected with the human A3 adenosine receptor using [125I]AB-MECA as radioligand. HE-NECA and NECA were the most potent compounds showing Ki values in the low nanomolar range, while the recently discovered non-xanthine A2A receptor antagonists ZM 241385, SCH 58261 and SCH 63390 showed affinity values in the micromolar range. These data further indicate the need to examine the affinity of new adenosine receptor ligands directly in human A3 receptors.

A2A-adenosine receptor reserve for coronary vasodilation

BACKGROUND

Adenosine is a potent coronary vasodilator and causes an increase of coronary blood flow by activation of A2A-adenosine receptors (A2A-AdoRs). The purpose of this study was to test the hypothesis that the high potency of adenosine and adenosine analogues to cause coronary vasodilation is explained by the presence of a large A2A-AdoR reserve ("spare receptors").

METHODS AND RESULTS

A novel, irreversible antagonist of A2A-AdoRs was used to inactivate receptors and reduce the response to agonist. Agonist-induced increases of coronary conductance before and after exposure of hearts to the irreversible antagonist were compared. Three agonists were studied: 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS21680), adenosine, and 2-chloro-N6-cyclopentyladenosine (CCPA). Data were analyzed to determine agonist KA (equilibrium dissociation constant) and EC50 values. Values of KA for activation of A2A-AdoRs by CGS21680, adenosine, and CCPA were 105, 1800, and 2630 nmol/L, respectively. In contrast, values of EC50 for CGS21680, adenosine, and CCPA to increase coronary conductance were 1.5, 85, and 243 nmol/L, respectively. By use of the law of mass action, it was calculated that half-maximal responses to CGS21680, adenosine, and CCPA occurred when only 1.3%, 5%, and 9%, respectively, of A2A-AdoRs were occupied by agonist.

CONCLUSIONS

Receptor reserves for 3 A2A-AdoR agonists were large. The receptor reserve for A2A-AdoRs to cause an increase of coronary conductance can explain both the high potency of adenosine to cause coronary vasodilation and the observation that an A2A-AdoR agonist can cause coronary vasodilation without systemic effects.

Synthesis and biological activity of a new series of N6-arylcarbamoyl, 2-(Ar)alkynyl-N6-arylcarbamoyl, and N6-carboxamido derivatives of adenosine-5'-N-ethyluronamide as A1 and A3 adenosine receptor agonists

A new series of 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ +-b earing N-arylureas or N-arylcarboxamido groups at the purine 6 position and N-arylureas combined with halogens or alkynyl chains at the 2 position have been synthesized and tested for affinity at A1 and A2A adenosine receptors in rat brain membranes and at cloned rat A3 receptors expressed in CHO cells. The derivatives contained the 5' substituent found in the potent, nonselective agonist 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ + (NECA). While the carboxamido derivatives (9-13) showed affinity for A1 receptors, the urea derivatives (30-45) showed different degrees of affinity and selectivity for the A3 adenosine receptor subtype. In particular the derivative bearing a p-sulfonamidophenyl-urea at the 6 position, 31 showed a high affinity (Ki = 9 nM) and selectivity for the A3 receptors compared to that of the reference compound 1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-be ta-D-ribofuranuronamide (IB-MECA). Furthermore, the importance of the stereochemistry in the interaction of these ligands at the rat A3 adenosine receptors has been evaluated by introducing a chiral chain at the 6 position. The introduction of halogens or alkynyl chains at the purine 2 position of selected ureas did not give the expected enhancement of potency at A2A and/or A3 receptors but rather showed a dramatic reduction of A2A affinity, resulting in compounds with good A2A/A3 selectivity. For example, the 2-(3-hydroxy-3-phenyl-1-propyn-1-yl)-6-(4-methoxyphenylurea) derivative 61 showed the capability to bind simultaneously to A1 and A3 receptor subtypes, excluding the A2A receptor. Compound 31 was shown to be an agonist, 9-fold more potent than NECA, at A3 receptors in rat RBL-2H3 mast cell membranes through stimulation of binding of [35S]GTP-gamma-S.

Design, synthesis, and biological evaluation of a second generation of pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines as potent and selective A2A adenosine receptor antagonists

New A2A adenosine receptor antagonists in the series of pyrazolo[4, 3-e]-1,2,4-triazolo[1,5-c]pyrimidines, bearing oxygenated substituents on the phenylalkyl chains on the 7-position, have been synthesized. The compounds were tested in binding and functional assays to evaluate affinity, potency, and selectivity for rat A2A compared to rat A1 and human A3 receptor subtypes. The most interesting compounds (5d,e,h) were tested also in binding to human A1 and A2A adenosine receptors. They showed very good affinity (Ki = 0.94 nM for compound 5h) and interesting selectivity with respect to both rA1 and hA3 (compound 5h: rA1/rA2A = 787, hA3/rA2A > 10 000). These important findings make this new series of compounds the first really selective for A2A adenosine receptors. Thermodynamic parameters were evaluated; all the tested compounds displayed an enthalpy-driven binding as expected for antagonists. Moreover, compound 5h showed a negative entropy value. The highly negative enthalpic and entropic contributions could mean that 5h fits very well in the binding site where, probably, an electrostatic interaction is present associated to a scarce solvent reorganization around the receptor binding site. These compounds deserve to be further developed to assess their potential for treatment of neurodegenerative disorders such as Parkinson's disease.

Heterocyclic analogs of DNA minor groove alkylating agents

It is generally accepted that neoplastic transformation is related to genes alteration or oncogene activation. In particular, DNA minor groove binding drugs have been extensively studied through the years in order to influence the regulation of gene expression by means of specific interactions with DNA bases moieties. Pyrrolo[2,1-c],[1,4].benzodiazepines (PBDs), CC-1065 and distamycins are three classes of minor groove binders which showed interesting cytotoxicity profiles, refined through already reviewed processes of SAR studies. Among the modifications to the three families of antitumor compounds, heterocyclic substitutions have been extensively applied by many groups in order to either modify the reactivity profile or introduce extra interactions within the minor groove, thus changing the binding site or modulating the binding sequence. The updated material related to these modifications has been rationalised and ordered to offer an overview of the argument.

Enzymatic synthesis of 2'-O-acyl prodrugs of 1-(beta-D-arabinofuranosyl)-5(E)-(2-bromovinyl)uracil and of 2'-O-acyl-araU, -araC and -araA

Pig liver esterase (EC 3.1.1.1) catalysed regioselective hydrolysis of 1-(2,3,5-tri-O-acyl-beta-D-arabinofuranosyl)uracil, -cytosine and -adenine to give the corresponding 2'-monoesters effectively and in high yield. This methodology enabled the preparation of 1-(2-O-acyl-beta-D-arabinofuranosyl)-5-[(E)-(2-bromovinyl)]uracil prodrugs which, although slightly less active than the parent 1-(beta-D-arabinofuranosyl)-5-(E)-(2 bromovinyl)uracil (sorivudine; BV-araU), were strongly active in vitro against varicella-zoster virus (ED50 2.4-45 ng/ml). The retarded rates of enzymatic hydrolysis of the 2'-esters imply that they might function as lipophilic prodrugs, leading to increased plasma and cellular concentrations. In view of the marked in vitro activity, they represent an interesting approach to arabinofuranosyl nucleoside prodrugs with improved pharmacokinetics and enzymatic stability.

Synthesis, cytotoxicity and antitumor activity of some new simplified pyrazole analogs of the antitumor agent CC-1065. Effect of an hydrophobic group on antitumor activity

Three simplified pyrazole analogs (7-9) of the antitumor agents CC-1065, were synthesized. In in vitro assays, against L1210 cell lines all derivatives showed a cytotoxicity in a pM range, values close to the natural target compound (+)-CC-1065. In in vivo tests, against disseminate L1210 leukemia cells, synthesized compounds showed a good potency (O.D. 300 micrograms/Kg) but no activity. These observations further validate the effect of the hydrophilic and/or hydrophobic characteristics of the substituents present on the molecules, confirming the relevance of this phenomena on in vivo activity. In fact in this case the increase of hydrophobic characteristics of the molecules produce the loss of activity, probably due to a worse bioavailability of the drugs in animals.

Synthesis, solvolytic stability and cytotoxicity of a modified derivative of CPzI, a pyrazole analog of the alkylation subunit of the antitumor agent CC-1065: effect of the nitrogen substitution on the functional reactivity

The synthesis and the comparative preliminary biological evaluation of a new pyrazole analog (16) of the CC-1065 alkylating unit (CPI) are described. This new derivative showed low cytotoxicity against L1210 murine leukemia (IC50 3064 nM) with respect to reference compound, but contrarily to literature data, was found to be more stable to solvolysis than the natural derivative (+/-)-N-Boc-CPI (pH 3, t1/2 = 212 h vs. 37 h). The results of such investigation showed that alkylation of the pyrazole nitrogen caused a loss of cytotoxic activity in vitro against tumor cells. This experimental observation allowed us to confirm the importance of free N-H for the anticellular activity.