New TFO conjugates containing a carminomycinone-derived chromophore.

Conjugates obtained by linking the anthracycline intercalating chromophore to triple helix forming oligonucleotides (TFOs) have been used in a physicochemical study of the stability of triple helices with DNA sequences of pharmacological relevance. The intercalating moiety is represented by carminomycinone derivatives obtained upon O-demethylation and hydrolysis of the glycosidic linkage of daunomycin followed by the introduction of an alkylating residue at two different positions. Results of experiments with a polypurinic region present in the multidrug resistance (MDR) gene indicate that the stability of the triple helix is significantly enhanced by replacement of C's with (5-Me)C's in the TFO sequences tested. The stability is not changed when a 3'-TpT is present in place of a 3'-CpG at the presumed intercalation site of the anthraquinone chromophore. The same carminomycinone derivatives were used for the preparation of conjugates able to form triple helices with the polypurine tract (PPT) present in the human integrated genome of HIV-1 infected cells. Three different TFOs (T(4)(Me)CT(4)(Me)CC, C2; T(4)(Me)CT(4)(Me)CC(Me)CC(Me)CCT, C6; and T(4)(Me)CT(4)G(6), G6) were designed and linked to the anthraquinone moiety. These conjugates showed a significantly enhanced ability to bind the PPT region of HIV with respect to the nonconjugated TFOs.

Adriamycin, 14-hydroxydaunomycin, a new antitumor antibiotic from S. peucetius var. caesius. Reprinted from Biotechnology and Bioengineering, Vol. XI, Issue 6, Pages 1101-1110 (1969).

Streptomyces peucetius var. caesius, obtained from S. peucetius, the daunomycin producing microorganism, by mutagenic treatment, differs from the parent culture by the color of the vegetative and aerial mycelia and by its antibiotic producing ability. S. peucetius var. caesius accumulates adriamycin in submerged and aerated culture on a medium containing glucose, brewer's yeast, and inorganic salts both in shake flasks and in stirred fermenters. Isolation of the product is performed by solvent extraction, chromatography on buffered cellulose columns, and crystallization as the hydrochloride. The new antitumor agent, adriamycin, is the 14-hydroxy derivative of daunomycin.

Synthesis and biological activity of the penem antibiotic MEN 10700 and its orally absorbed ester MEN 11505.

The synthesis and biological properties of the new penem antibiotic MEN 10700 (6) and of its selected oral prodrug MEN 11505 (8f) are described. MEN 10700 showed a broad spectrum of activity, with high potency both on Gram-positive and Gram-negative strains. It also exhibited good antibacterial activity toward anaerobes and on strains selected for their resistance to other antibacterial agents (cefotaxime- or ceftazidime-resistant Gram-negative strains, ciprofloxacin-resistant E. coli, extended spectrum beta-lactamase producing and cephalosporinase inducible enterobacteria). MEN 10700 showed a very high stability to enzymatic degradation by renal dehydropeptidase DHP-I. After oral administration in rats of the pivaloyloxymethyl ester prodrug MEN 11505, the relative bioavailability of MEN 10700 was calculated as F=43%.

Configurational requirements of the sugar moiety for the pharmacological activity of anthracycline disaccharides.

The amino sugar is recognized to be a critical determinant of the activity of anthracycline monosaccharides related to doxorubicin and daunorubicin. In an attempt to improve the pharmacological properties of such agents, novel anthracycline disaccharides have been designed in which the amino sugar, daunosamine, is separated from the aglycone by another carbohydrate moiety. In the present study, we examined the influence of the orientation of the second sugar residue on drug biochemical and biological properties in a series of closely related analogs. This structure-activity relationship study showed that the substitution of the daunosamine for the disaccharide moiety dramatically reduced the cytotoxic potency of the drug in the 4-methoxy series (daunorubicin analogs). In contrast, in the 4-demethoxy series (idarubicin analogs), the C-4 axial, but not the equatorial, configuration conferred a cytotoxic potency and antitumor activity comparable to that of doxorubicin. The configuration also influenced the drug's ability to stimulate topoisomerase II alpha-mediated DNA cleavage. Indeed, the glycosides with the equatorial orientation were ineffective as topoisomerase II poisons, whereas the compounds with axial orientation were active, although the daunorubicin analog exhibited a lower activity than the idarubicin analog. It is conceivable that the axial orientation allows an optimal interaction of the drug with the DNA-enzyme complex only in the absence of the methoxy group. Our results are consistent with a critical role of the sugar moiety in drug interaction with the target enzyme in the ternary complex.

Improved efficacy and enlarged spectrum of activity of a novel anthracycline disaccharide analogue of doxorubicin against human tumor xenografts.

On the basis of a structure-activity study of a new series of anthracycline disaccharides, we recently identified a doxorubicin analogue (MEN 10755) with a promising antitumor activity. In the present study, to better support the pharmacological interest of MEN 10755, we extended the preclinical evaluation of antitumor efficacy to a large panel of 16 human tumor xenografts, which originated from different clinicopathological types. Tumors with typical multidrug-resistant phenotype were excluded because MEN 10755 was found unable to overcome resistance mediated by transport systems. In the doxorubicin-responsive series, MEN 10755 exhibited a higher activity in three of five tumors, as documented by a more marked tumor growth inhibition and an increased value of log-cell kill. In the series of doxorubicin-resistant tumors, MEN 10755 was found effective in 6 of 11 tumors (1 breast, 3 lung, and 2 prostate carcinomas). The overall response rates were 31% and 69% for doxorubicin and MEN 10755, respectively. The improvement in drug efficacy was also supported by a substantial increase in the long-term survivor rate of animals implanted with responsive tumors. Most of the tumors refractory to doxorubicin and responsive to MEN 10755 were characterized by overexpression of the antiapoptotic protein Bcl-2. In one of these tumors (MX-1 breast carcinoma), we examined the ability of MEN 10755 to induce phosphorylation of Bcl-2 after a single treatment with therapeutic doses. The results indicated that, unlike doxorubicin, MEN 10755 induced protein phosphorylation. A similar modification was produced by Taxol, which is known to be very effective against the tumor. The correlation between drug efficacy and Bcl-2 phosphorylation may underly a peculiar feature related to improvement of efficacy of the disaccharide analogue. In conclusion, the present study supports some favorable features of the novel doxorubicin analogue in terms of both efficacy and tolerability with comparison to doxorubicin, although the improvement is somewhat tumor- and schedule-dependent.

Biosynthetic anthracyclines.

This review summarizes the structure, the occurrence and the available data concerning the bioactivity of biosynthetic anthracyclines. The anthracyclines represent an important family of natural products produced by microorganisms of Streptomyces and related genera and include clinically useful agents for the medical treatment of human cancer. Chemically, the anthracyclines are glycosides characterized by a quinone tetracyclic aglycone and one or more deoxysugar units, mostly belonging to the L-hexopyranoside series, comprising generally an aminosugar. The different compounds belonging to this family are structurally related as they share a common biosynthetic pathway. Although some statements concerning structure activity relationships and molecular requirements for activity can be made, published data are not adequate for the comparative evaluation of potential antitumor efficacy of biosynthetic anthracyclines. This family of natural products is therefore still open for pharmacological investigation.

MEN 10700, a new penem antibiotic: in-vitro activity and its correlation with beta-lactamase stability, PBP affinity and diffusion through the bacterial cell wall.

The in-vitro activity of MEN 10700, a novel penem, was compared with that of imipenem, ritipenem, ampicillin/sulbactam, cefotaxime, ciprofloxacin and amikacin against 1088 strains taken from 21 genera, including Gram-negative, Gram-positive and anaerobic bacteria. MIC data showed that MEN 10700 was very active against staphylococci and streptococci (MIC90 < or = 0.5 mg/L) and against most members of the Enterobacteriaceae (MIC90 < or = 2 mg/L), with reduced activity only against Providencia stuartii (MIC90 = 8 mg/L). MEN 10700 was also active against anaerobic species such as Clostridium perfringens and Bacteroides fragilis as well as Moraxella catarrhalis. It was moderately active against Enterococcus faecalis and inactive against Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Aeromonas spp. and Acinetobacter spp. Its antibacterial spectrum was thus slightly narrower than that of imipenem, but compared favourably with those of a third-generation cephalosporin and ritipenem. MEN 10700 was highly stable to a number of beta-lactamases and was a poor inducer of class I enzymes. It bound penicillin-binding protein 2 with the highest affinity and easily permeated the outer membrane of Escherichia coli.

From the pigments of the actinomycetes to third generation antitumor anthracyclines.

After the assessment of the antitumor activity of the anthracycline pigments, the S peucetius group of metabolites was discovered and eventually doxorubicin, a major anticancer agent of established clinical usefulness was developed in the early seventies. A second generation of compounds followed, represented mainly by the better tolerated epirubicin and by the highly potent antileukemic drug, idarubicin. This was the result of a wide program of analog development that provided the basis for further investigations concerning both the study of structure-activity relationships and the synthesis of novel promising derivatives including the 8- and 10-fluoro compounds and the disaccharides. A member of the latter group, namely 7-O-(4'-O-alpha-L-daunosaminyl-2'-deoxy- alpha-L-fucosyl)-4-demethoxyadriamycinone, is undergoing clinical trials as a third generation antitumor anthracycline.

MEN 11420 (Nepadutant), a novel glycosylated bicyclic peptide tachykinin NK2 receptor antagonist.

1. The pharmacological profile was studied of MEN 11420, or cyclo[[Asn(beta-D-GlcNAc)-Asp-Trp-Phe-Dap-Leu]cyclo(2beta-5beta )], a glycosylated derivative of the potent, selective, conformationally-constrained tachykinin NK2 receptor antagonist MEN 10627 (cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2beta-5beta)). 2. MEN 11420 competitively bound with high affinity to the human NK2 receptor stably transfected in CHO cells, displacing radiolabelled [125I]-neurokinin A and [3H]-SR 48968 with Ki values of 2.5+/-0.7 nM (n = 6) and 2.6+/-0.4 nM (n = 3), respectively. 3. MEN 11420 showed negligible binding affinity (pIC50 < 6) at 50 different receptors (including tachykinin NK1 and NK3 receptors) and ion channels. 4. In the rabbit isolated pulmonary artery and rat urinary bladder MEN 11420 potently and competitively antagonized tachykinin NK2 receptor-mediated contractions (pK(B) = 8.6+/-0.07, n = 10, and 9.0+/-0.04, n = 12; Schild plot slope = -1.06 (95% c.l. = -1.3; -0.8) and -1.17 (95% c.l. = -1.3; -1.0), respectively). MEN 11420 produced an insurmountable antagonism at NK2 receptors in the hamster trachea and mouse urinary bladder. However, in both preparations, the effect of MEN 11420 was reverted by washout and an apparent pK(B) of 10.2+/-0.14, n = 9, and 9.8+/-0.15, n = 9, was calculated in the hamster trachea and mouse urinary bladder, respectively. 5. MEN 11420 showed low affinity (pK(B) < 6) at guinea-pig and rat tachykinin NK1 (guinea-pig ileum and rat urinary bladder) and NK3 (guinea-pig ileum and rat portal vein) receptors. On the whole, the affinities (potency and selectivity) showed by MEN 11420 for different tachykinin receptors, measured either in binding or in functional bioassays, were similar to those shown by the parent compound, MEN 10627. 6. The in vivo antagonism of the contractions produced by [betaAla8]neurokinin A(4-10) (1 nmol kg(-1)) was observed after intravenous (dose range: 1-10 nmol kg(-1)), intranasal (3-10 nmol kg(-1)), intrarectal (30-100 nmol kg(-1)) and intraduodenal (100-300 nmol kg(-1)) administration of MEN 11420. MEN 11420 was more potent (about 10 fold) and longer lasting than its parent compound MEN 10627, possibly due to a greater metabolic stability. 7. A dose of MEN 11420 (100 nmol kg(-1), i.v.), that produced potent and long lasting inhibition of the contraction of the rat urinary bladder induced by challenge with the NK2 selective receptor agonist [betaAla8]neurokinin A(4-10) (10-300 nmol kg(-1)), was without effect on the responses produced by the NK1 receptor selective agonist [Sar9]substance P sulphone (1-10 nmol kg(-1)). 8. These findings indicate that MEN 11420 is a potent and selective tachykinin NK2 receptor antagonist. The introduction of a sugar moiety did not produce major changes in the affinity profile of this antagonist as compared to MEN 10627, but markedly improved its in vivo potency and duration of action. With these characteristics, MEN 11420 is a suitable candidate for studying the pathophysiological significance of tachykinin NK2 receptors in humans.

Non-covalent complexes between DNA-binding drugs and double-stranded deoxyoligonucleotides: a study by ionspray mass spectrometry.

The non-covalent complexes between some DNA-binding drugs and duplex oligodeoxynucleotides were studied by ionspray mass spectrometry, with the aim of evaluating the suitability of this technique to screen rapidly a series of drugs exerting their activity through non-covalent binding to specific base sequences of DNA. Two classes of drugs were considered, distamycins (which show affinity for the minor groove of DNA) and anthracyclines (which interact through intercalation between bases). For the former, d(CGCGAATTCGCG)2 was chosen as the model oligodeoxynucleotide. Following optimization of sample preparation and instrumental conditions, the complexes of different distamycins were observed; depending on the ligand considered, 1:1 or 2:1 complexes were formed preferentially. A semi-quantitative evaluation of the relative affinities was made by measuring the ratio of the complexes signals to those of the duplex, and also by competitive binding with equimolar amounts of distamycin. For anthracyclines, the daunorubicin-d(CGATCG)2 complex was chosen as the model for a preliminary mass spectrometric study; however, the signals of the duplex and the complex were very low compared with the monomer signal. Since the complex was known to be stable in solution, this was ascribed to gas-phase instability, probably caused by electrostatic repulsion between negatively charged phosphate groups.

Doxorubicin disaccharide analogue: apoptosis-related improvement of efficacy in vivo.

BACKGROUND: Although doxorubicin remains one of the most effective agents for the treatment of solid tumors, there is an intensive effort to synthesize doxorubicin analogues (compounds with similar chemical structures) that may have improved antitumor properties. We have synthesized a novel doxorubicin disaccharide analogue (MEN 10755) and have characterized some of its relevant biochemical, biologic, and pharmacologic properties. METHODS: The antitumor activity of this compound (MEN 10755) was studied in a panel of human tumor xenografts, including xenografts of A2780 ovarian tumor cells, MX-1 breast carcinoma cells, and POVD small-cell lung cancer cells. MEN 10755 was compared with doxorubicin according to the optimal dose and schedule for each drug. The drug's cytotoxic effects, induction of DNA damage, and intracellular accumulation were studied in A2780 cells. DNA cleavage mediated by the enzyme topoisomerase II was investigated in vitro by incubating fragments of simian virus 40 DNA with the purified enzyme at various drug concentrations and analyzing the DNA cleavage-intensity patterns. Drug-induced apoptosis (programmed cell death) in tumors was determined with the use of MX-1 and POVD tumor-bearing athymic Swiss nude mice. RESULTS: MEN 10755 was more effective than doxorubicin as a topoisomerase II poison and stimulated DNA fragmentation at lower intracellular concentrations. In addition, MEN 10755 exhibited striking antitumor activity in the treatment of human tumor xenografts, including those of the doxorubicin-resistant breast carcinoma cell line MX-1. CONCLUSIONS: The high antitumor activity of MEN 10755 in human tumor xenografts, including doxorubicin-resistant xenografts, and its unique pharmacologic and biologic properties make this disaccharide analogue a promising candidate for clinical evaluation.

Synthesis and binding properties of conjugates between oligodeoxynucleotides and daunorubicin derivatives.

Conjugation of an anthracycline to a triplex-forming oligonucleotide (TFO) allows delivery of this drug to a specific DNA site, preserving the intercalation geometry of this class of anticancer agents. Conjugate 11, in which the TFO is linked via a hexamethylene bridge to the O-4 on the D ring of the anthraquinone moiety, affords the most stable triple helix, through intercalation of the planar chromophore between DNA bases and binding of both the TFO and the amino sugar to the major and the minor groove respectively.

Role of apoptotic response in cellular resistance to cytotoxic agents.

The development of drug resistance is a major obstacle to effectiveness of chemotherapeutic treatment of human tumors with cytotoxic agents. Drug resistance is described as a multifactorial phenomenon, involving the expression of defense factors and/or detoxification mechanisms, alterations in drug-target interactions, and cellular response to specific cytotoxic lesions (in particular, DNA damage). Although the proposed mechanisms may contribute to the development of a variable degree of cellular resistance, it is possible that the cell response (i.e., DNA repair or apoptosis) following DNA damage plays a critical role in determining cellular chemosensitivity. The preclinical observations that tumor response to effective drug treatments is associated with induction of apoptosis support the possibility that a decreased susceptibility to apoptosis (apoptosis resistance) is relevant to clinical resistance. A number of molecular alterations associated with transformation and/or tumor progression may also be implicated in regulation of cell death pathways and in the development of drug resistance. There is evidence that the wild-type p53 is involved in cellular response to DNA damage, including cell cycle regulation, DNA repair, and activation of the pathway leading to apoptosis. Loss of wild-type p53 function could cause resistance to DNA-damaging agents, as a consequence of abrogation of p53-dependent apoptosis. The identification of new agents able to trigger p53-independent apoptosis and the search for biochemical modulators downstream of p53 may be of clinical relevance because many tumors are deficient in p53 function due to mutation or deletion. An overview of the resistance mechanisms is presented, with particular reference to the role of p53 mutations in clinical resistance and of apoptosis-related genes in cellular chemosensitivity.

New developments in antitumor anthracyclines.

Doxorubicin is a major anticancer agent introduced to extended clinical use in the early 1970s. The fulfillment of a wide program of analogue synthesis led to the development of the better tolerated epirubicin and of a highly potent antileukemic drug, idarubicin. In recent years, on the basis of the available information on the molecular requirements for action, a new synthetic program, coupled with target-oriented pharmacological experiments, was carried out. Various interesting derivatives, namely, the 8- and 10-fluoro compounds and the disaccharides, were obtained. The latter compounds exhibited a strong dependence of biological activity on the orientation (axial vs. equatorial) of the second sugar moiety, daunosamine. A member of this group, namely, 7-O-(4'-O-alpha-L-daunosaminyl-2'-deoxy-alpha-L-fucosyl)-4-demetho xy-adriamycinone, is presently undergoing clinical trials as a third generation antitumor anthracycline.

Deformyldistamycin-DNA interaction; DNA conformational changes as revealed by titration rotational viscometry.

The conformational changes of a natural DNA species on binding of deformyl-distamycin (dDst) have been analysed, at 22 degrees C and 7.6 degrees C, in terms of changes of apparent persistence length (a) and of apparent contour length (L), by means of titration rotational viscometry with both high and low molar mass calf thymus (ct) DNA molecules. Next to ligand binding mediated alterations in DNA stiffness, changes of a are the result of helix bending and also of unbending of intrinsic helix bends. A test for the latter are viscosity measurements at different temperatures. Changes of L, on binding of non-intercalating ligands, are interpreted as the result of changes in the intrinsic solenoidal structure components of the natural eukaryotic DNA. Such tertiary-structure components do exist if base sequence dependent helix bends of (nucleosomal) DNA are phased with the helix screw [Drew & Travers, JMB 186, 773 (1985); Reinert et al., JBSD 9, 537 (1991)]. Hence, the measured very small changes of L at ligand/DNA-P ratios r < 0.02 are mainly understood as a partial abolition of intrinsic tertiary structure components and the following negative ones as a respective reinforcement of such structures by dDst binding to AT rich binding sites. Several r-intervals with different slope of the viscosity changes could be resolved at r < 0.05. The resolution of more than four modes of dDst interaction with ctDNA at very low r values is comparable to DNA interaction of Nt and several other ligands but not of distamycin. Advanced titration rotational DNA-viscometry is again able to resolve subtle quantitative details of ligand mediated DNA conformational changes of high stereochemical relevance.

Biochemical and pharmacological activity of novel 8-fluoroanthracyclines: influence of stereochemistry and conformation.

In an attempt to better understand the role of the cyclohexene ring (ring A) in the biochemical and pharmacological properties of anthracyclines related to doxorubicin and daunorubicin, we investigated the effects of introduction of a fluorine atom at position 8 of idarubicin (4-demethoxydaunorubicin) on drug molecular conformation and biochemical and pharmacological activities. The study showed that the stereochemistry of the substituent at position 8 influenced the "half-chair" conformation, so that in the (8R)-fluoroepimer the A ring retained the alpha half-chair conformation, which is the most stable for natural compounds (i.e., daunorubicin and doxorubicin), and the (8S)-fluoroepimers preferred the beta half-chair conformation. The (8R)-fluoroepimer was more effective than the (8S)-fluoroepimer and idarubicin in stimulating topoisomerase II-mediated DNA cleavage. Similarly, the epimer with the alpha conformation was markedly more potent than the (8S)-epimer as a cytotoxic agent in a variety of human tumor cell lines and was more effective as an antitumor agent in the treatment of an ovarian carcinoma xenograft. In addition, 8-fluoro derivatives were able to overcome the resistance to doxorubicin in a number of human tumor cell lines expressing different mechanisms of resistance. In conclusion, these findings provide evidence that drug interactions involving the external (nonintercalating) moiety of the anthracycline chromophore play an important role in determining pharmacological properties, including drug ability to induce DNA cleavage, and therefore their antitumor efficacy.

Synthesis and antibacterial activity of C-4 thio- and dithiocarbamate monobactam derivatives.

New series of monobactam antibiotics, bearing thio-and dithiocarbamate derivatives as C-4 side chain, were synthesized. Some compounds were found to have good antibacterial activity against Gram-negative bacteria.

Backbone and benzoyl mustard carrying moiety modifies DNA interactions of distamycin analogues.

Alkylating distamycin derivative FCE-24517 (l) is the prototype of a novel class of alkylating agents. In the present study we have investigated the effect of further chemical modifications introduced in the alkylating distamycin-derived molecule with the aim of improving their ability to bind DNA. The new compound, MEN 10710 (II), has a four pyrrolecarboxamide backbone linked at its N-terminus and through a butanamido residue to a 4-[bis(chloroethyl)amino]phenyl moiety. We have demonstrated that the presence of the flexible trimethylene chain confers to the novel distamycin derivative a peculiar mode of interaction with DNA as compared with I or melphalan. In fact, interstrand cross-links are detected in DNA samples treated even with low concentrations of II (being 200-fold more efficient than melphalan) but not with I. Similar results were obtained with a related compound of II containing a three pyrrole ring backbone. Compound II induces a conformational change in the DNA structure as deduced from the inhibition of T4 DNA ligase activity. In alkylation experiments, unlike melphalan, both I and II induce DNA breaks at bases closely located to AT-rich tracts, however II was more potent than I in producing greater amount of covalent adducts. These data suggest that the new compound shows a different and peculiar mechanism of interaction with DNA.

Structure-activity relationship of new 2-substituted penem antibiotics.

The antibacterial activities of three new penems with 4-hydroxyprolinamide, 1-prolinamide and N-methyl-N-2-propionamide substituents, respectively, in position 2 and of their stereoisomers were examined against Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, Escherichia coli and Pseudomonas aeruginosa. All substitutes conferred a broad antibacterial spectrum on the penem moiety. Changes in stereoisomerism selectively improved the activity against E. coli, S. aureus or enterococci. The structure-activity relationships of each compound were discussed in relation to minimum inhibitory concentrations, penicillin-binding protein (PBP) affinity and outer membrane permeability coefficient in E. coli. In this microorganism, PBP 2 was the target for all compounds. Changes in stereoisomerism influenced the affinity for PBPs 1A/B and 2. All antibiotics easily permeated the outer membrane of E. coli and, within each group of compounds, the penetration rate correlated with the antibacterial activity.

Synthesis and biological evaluation of novel NK-1 tachykinin receptor antagonists: the use of cycloalkyl amino acids as a template.

In the course of a program aimed at synthesizing novel, potent NK-1 tachykinin receptor antagonists, we developed upon a bioactive model by comparing the low energy structures of a series of peptide and nonpeptide Substance P antagonists. The comparison was based on the superimposition of the aromatic rings, assuming that the rest of the molecule behaves predominantly as a template to arrange the key aromatic groups in the right spatial position. A series of 2-aminocyclohexane carboxylic acid analogues were then selected as the best templates for reproducing the postulated bioactive structure, leading to several pseudo-peptides with interesting biological activity. According to the molecular modeling, these compounds exhibit a neat parallel facing of the indolyl and naphthyl groups at about 3 A distance. Ultraviolet absorption and steady state fluorescence measurements support this conclusion, showing a linear correlation between the spectral properties and the binding affinity of these analogues. Stacking of the indole ring with naphthalene gives rise to a complex characterized by a well-defined molar extinction coefficient. Consistently, steady state and lifetime fluorescence measurements suggest that the quenching process is ascribable to ground-state interactions between the chromophores. Implications of the pi stacking propensity of aromatic groups in the biological activity of the compounds examined are briefly discussed.