Synthesis, DNA binding, cytotoxicity and sequence specificity of a series of imidazole-containing analogs of the benzoic acid mustard distamycin derivative tallimustine containing an alkylating group at the C-terminus

In an attempt to produce additional alkylation and crosslinking in the minor groove of DNA, imidazole-containing analogs of distamycin were synthesized with benzoic acid mustard (BAM) and methoxyaziridinyl moieties present at the N- and C-termini, respectively. Analogs 1a-c differed in the number of methylene units (2-4 respectively) between the C-terminal carbonyl group and the methoxyaziridinyl moiety. DNA binding affinity to several polynucleotides decreased with increasing linker length, whereas DNA interstrand crosslinking ability, as measured by a plasmid gel based assay, increased. The in vitro cytotoxicity in human chronic myeloid leukemia K562 cells and the panel of human tumor cell lines at the National Cancer Institute decreased with increasing number of methylene units, and no increase in cytotoxicity was observed over compound AR-1-122 which did not contain the methoxyaziridinyl moiety. 1a-c had the same sequence selectivity of alkylation as AR-1-122, showing alkylation only at 5'-TTTTGPu sequences. The relative binding to these sequences decreased with increasing number of methylene units. The addition of a methoxyaziridinyl moiety in this group of imidazole and BAM-containing compounds can, therefore, increase crosslinking ability to naked DNA but this does not result in an increase in cytotoxicity. In contrast the cytotoxicity was related to their ability to produce sequence specific alkylation at 5'-TTTTGPu sequences.     

Synthesis and antitumor activity of novel benzophenone derivatives

Novel benzophenone derivatives were synthesized and screened for cytotoxic and antitumor activity. Friedel-Crafts condensation was employed to construct the benzophenone skeleton. Among the compounds synthesized, morpholino and thiomorpholino benzophenones 3a-d exhibited potent cytotoxic activity against P388 murine leukemia and PC-6 human lung carcinoma cells in vitro, and compounds 3a, 3c, and 3j, when administered intraperitoneally, showed significant antitumor activity against the malignant ascites caused by intraperitoneal inoculation of P388 cells in mice.     

MST-16, a novel derivative of bis(2,6-dioxopiperazine), synergistically enhances the antitumor effects of anthracyclines

OBJECTIVE: The aim of this study was to evaluate whether toluene, like many other organic solvents and solvent mixtures, could impair color vision. SUBJECTS AND METHODS: We investigated color vision impairment in three groups of workers, two groups occupationally exposed to toluene and a nonexposed group. The first exposed group, group E1, comprised 41 workers (median value of toluene in air 35.00 ppm, range 11.3-49.3 ppm) and the second exposed group, group E2, comprised 32 subjects (median value of toluene in air 156.00 ppm, range 66.0-250.0 ppm). The nonexposed group, group NE, comprised 83 subjects. Color vision was evaluated by the Lanthony D-15 desaturated test according to Verriest's classification: type I, loss in the red-green range; type II, loss in the blue-yellow and red-green ranges, and type III, loss in the blue-yellow range. Subjects were classified as dyschromates if specific acquired loss was determined in at least one eye. In both exposed groups, exposure was evaluated by measurement of the concentration of toluene in the ambient air and in the blood. In group E2, level of hippuric acid and orthocresol in urine after the work shift were also determined. The Mann-Whitney U-test, t-test, chi 2-test, and Spearman's rank correlation and multiple regression analysis were used for statistical analysis. RESULTS: Type III dyschromatopsia was detected in all groups examined: 26.6% of the workers in group NE, 31.7% of those in group E1, and 50% of those in group E2. As many as 15.6% of the workers in group E2, 4.8% of those in group E1, and only 1.2% of those in group NE had type II dyschromatopsia. A statistically significant difference in the prevalence of total dyschromatopsia (type III + type II) was established among the three examined groups together (chi 2 = 14.13; df = 2; P < 0.01), between group E2 and group E1 (chi 2 = 4.96; P < 0.05), and between group E2 and group NE (chi 2 = 12.50; P < 0.005), whereas no significant difference was found between groups E1 and NE. Type III dyschromatopsia was significantly correlated with age in group NE (P < 0.01) and in group E1 (P < 0.005). In group E2, both type II (P < 0.05) and type III dyschromatopsia correlated with toluene in ambient air and with the duration of exposure to toluene (both P < 0.005). In group E2, total dyschromatopsia correlated significantly with toluene in ambient air and in blood (both P < 0.05) as well as with hippuric acid in urine after the work shift (P < 0.001). CONCLUSION: This study suggests that toluene can impair color vision.     

Antimalarial activity of synthetic analogues of distamycin

Malaria, one of the most serious diseases transmitted by arthropods, is largely present in tropical and even temperate zones in endemic or epidemic form. More than 40% of the world's population lives in areas at risk for exposure, and the World Health Organization reports that approximately 300 million people are affected by the infection (mostly caused by the species Plasmodium falciparum), with 1-2 million deaths per year. These data, and the fact that malaria is becoming increasingly refractory to treatment through resistance of the parasite to antimalarial agents currently in use, e.g., chloroquine, emphasize the need to develop new drugs. The well-known antiparasitic activity of oligopyrrolamidine natural products, such as distamycin and netropsin, suggested the antimalarial evaluation of related compounds obtained by new chemical modifications. Besides possessing antiviral and antitumoural properties, distamycin exhibits interesting in vitro activity against P. falciparum. Unfortunately, the high toxicity associated with this product precludes its development as a drug. However, some synthetic analogues of distamycin proved to be highly active against chloroquine-sensitive and -resistant strains of P. falciparum, besides showing low toxicity in vitro.     

Synthesis of a novel phosphate ester of a vitamin E derivative and its antioxidative activity

A novel phosphate ester containing a chromanol structure was synthesized from 1,2-diacyl-sn-glycero-3-phospho-2'-hydroxyethyl-2',5',7',8'-tetramethyl- 6' -hydroxychroman (PCh) by hydrolysis catalyzed by phospholipase C from Bacillus cereus. The structure of the product was found by spectral analyses to be 2-(2',5',7',8'-tetramethyl-6'-hydroxychromanyl)ethylphosphate++ + (Ch-P). Ch-P was highly soluble in the aqueous phase at neutral pH values and exerted higher antioxidative activity than alpha-tocopherol and PCh in the Fe(III)/ascorbic acid-catalyzed peroxidation of a fish oil emulsion and the autoxidation of a rat brain homogenate.     

Synthesis and bioreductive potential of a mono N-oxide derivative of the alkylating agent chlorambucil

Chlorambucil N-oxide (CHLN-O) was synthesized and evaluated for in vitro bioreductive antitumor activity. A time-dependent hypoxic differential was observed when EMT6 cells were exposed to CHLN-O in the presence of rat liver microsomes and reducing equivalents. The cytotoxicity of the N-oxide was potentiated under hypoxia, and augmented further by a combination of low pH and hypoxia. Metabolic studies were also undertaken, which utilized previously described HPLC methodology for the analysis of CHLN-O loss from biological fluids. These demonstrated the requirement for microsomal enzymes and reducing equivalents, and also illustrated the time-dependent manner of CHLN-O loss from isolated microsomal preparations.     

Synthesis and evaluation of novel rhodacyanine dyes that exhibit antitumor activity

Rhodacyanine dyes and several analogous delocalized lipophilic cations (DLCs) were synthesized and evaluated as novel antitumor agents. Rhodacyanine dye consists of two heteroaromatic rings such as thiazoles at both termini of the conjugate systems and 4-oxothiazolidine (rhodanine) in the middle of it. Compounds with such a unique double-conjugate structure were found to inhibit the growth of several tumor cell lines, such as colon carcinoma CX-1, and to exhibit relatively low toxicity against normal kidney cell line CV-1 (e.g., IC50(CX-1) = 50 nM, IC50(CV-1) = 17.3 microM; selectivity index = 346 for compound 5). These compounds were also found to be efficacious in the tumor-bearing nude mice model (e.g., against human melanoma LOX; T/C (%) = 168 for compound 5). Structural modifications on rhodacyanine, including deletion of a heteroaromatic ring involved in the merocyanine conjugate system and replacement of rhodanine with a structurally related moiety such as 4-oxoimidazolidine or 4-oxo-1,3-dithiolane, resulted in a loss of the selectivity and/or the activity. Our current structure-activity studies imply that the double-conjugate system with a rhodanine moiety is essential for the selective activity of rhodacyanine dyes, and we find this class of compounds as unique antitumor agents candidates.     

Homocamptothecins: synthesis and antitumor activity of novel E-ring-modified camptothecin analogues

Homocamptothecin (hCPT), a camptothecin (CPT) analogue with a seven membered beta-hydroxylactone which combines enhanced plasma stability and potent topoisomerase I (Topo I)-mediated activity, is an attractive template for the elaboration of new anticancer agents. Like CPT, hCPT carries an asymmetric tertiary alcohol and displays stereoselective inhibition of Topo I. The preparation and biological screening of racemic hCPT analogues are described. The 10 hCPTs tested were better Topo I inhibitors than CPT. Fluorinated hCPTs 23c, d,f,g were found to have potent cytotoxic activity on A427 and PC-3 tumor cell lines. Their cytotoxicity remained high on the K562adr and MCF7mdr cell lines, which overexpress a functionally active P-glycoprotein. Fluorinated hCPTs were more efficacious in vivo than CPT on HT-29 xenografts. In this model, a tumor growth delay of 25 days was reached with hCPT 23g at a daily dose of 0.32 mg/kg, compared to 4 days with CPT at 0.625 mg/kg. Thus difluorinated hCPT 23g warrants further investigation as a novel Topo I inhibitor with high cytotoxicity toward tumor cells and promising in vivo efficacy.     

MEN 10,573 and MEN 10,612, novel cyclic pseudopeptides which are potent tachykinin NK-2 receptor antagonists

The activity and selectivity of MEN 10,573 and MEN 10,612, novel cyclic pseudopeptides which are selective tachykinin NK-2 receptor antagonists is described, as compared to that of previously characterized linear and cyclic compounds. For the NK-2 receptor, the activity of test compounds was investigated in the hamster isolated trachea (HT) and the endothelium-deprived rabbit isolated pulmonary artery (RPA), two preparations which are endowed with pharmacologically distinct forms of the NK-2 receptor. The novel cyclic pseudopeptides, MEN 10,573 and MEN 10,612 displayed very high affinity for the NK-2 receptor in the HT (pA2 8.66 and 9.06, respectively) which is higher than that observed in the RPA (pA2 7.31 and 7.41 for MEN 10,573 and MEN 10,612, respectively). The antagonism exerted by MEN 10,573 and MEN 10,612 was of competitive nature in both preparations. MEN 10,573 and MEN 10,612 also displayed competitive antagonism for NK-2 receptor-mediated responses in the rabbit bronchus (RB), rat vas deferens (RVD), circular muscle of the human colon (HUC) and ileum (HUI). In the RB, HUC and HUI, the potency of the novel cyclic pseudopeptides was comparable to that of MDL 29,913 and about 10-fold greater than that of L659,877. In the RVD however, the potency of MEN 10,573 MEN 10,612 or MDL 29,913 was similar to that of L659,877. In anaesthetized rats, i.v. injection of MEN 10,612 produced a selective and long-lasting blockade of the urinary bladder contraction produced by the i.v. injection of the NK-2 receptor selective agonist [beta Ala8]neurokinin A(4-10), without affecting the response to the NK-1 receptor selective agonist [Sar9]substance P sulfone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structure-activity relationship studies of novel somatostatin analogs with antitumor activity

A series of new somatostatin analogs were synthesized in order to study the relative importance of specific substitutions in relation to selectivity between their endocrine and antitumor effects. Substitutions were carried out in all positions, except for Lys in position 5. Peptides were tested for their ability to inhibit in vitro and in vivo GH release, proliferation of the MCF 7 breast carcinoma cell line and tyrosine kinase activity in the HT 29 human colon carcinoma cell line. Selective biological activity was achieved in GH release and antitumor activity by the different amino acid substitutions. One of the analogs, with a five-residue ring (D-Phe-Cys-Tyr-D-Trp-Lys-Cys-Thr-NH2, TT-232), was unique. It had no GH release inhibitory activity, but did have strong tyrosine kinase inhibitory and antiproliferative effects.     

Anti-inflammatory and analgesic effects of a novel pyrazole derivative, FR140423

The pharmacological profile of a novel and newly discovered non-steroidal anti-inflammatory and analgesic compound, 3-(difluoromethyl)-1-(4-methoxyphenyl)-5-[4-(methylsulfinyl)phenyl]pyraz ole (FR140423), was investigated. In recombinant human cyclooxygenase enzyme assays, the inhibition of prostaglandin E2 formation by FR140423 was 150 times more selective for cyclooxygenase-2 than cyclooxygenase-1. Oral administration of FR140423 dose dependently reduced carrageenin-induced paw edema and adjuvant arthritis. These effects were two- to three-fold more potent than those of indomethacin. Unlike indomethacin, FR140423 did not induce mucosal lesions in the stomach. FR140423 showed dose-dependent anti-hyperalgesic effects in the yeast-induced hyperalgesic model. This effect was five-fold more potent than that of indomethacin. Furthermore, FR140423 increased the pain threshold in non-inflamed paws and, unlike indomethacin, it produced an analgesic effect in the tail-flick test. These analgesic effects were blocked by the mu-opioid antagonist naloxone. These results suggest that FR140423, a selective cyclooxygenase-2 inhibitor, is a potent non-steroidal anti-inflammatory drug (NSAID) without gastrointestinal side effects and is a unique compound having morphine-like analgesic effects.     

Phase I and pharmacologic study of penclomedine, a novel alkylating agent, in patients with solid tumors

PURPOSE: To determine the maximum-tolerated dose (MTD), principal toxicities, and pharmacologic behavior of penclomedine, a novel alkylating agent. PATIENTS AND METHODS: Penclomedine (45 to 550 mg/ m2/d every 3 weeks) was administered as a 1- or 3-hour intravenous (IV) infusion for 5 consecutive days to patients with solid tumors. RESULTS: On a 1-hour dosing schedule, ataxia, vertigo, nystagmus, and a motor aphasia were the principal toxicities of penclomedine. These neurologic effects were dose-related, and evolved from complaints of somnolence and dizziness, to more pronounced signs and symptoms of cerebellar dysfunction. Up to and including doses of 415 mg/m2, these effects were well tolerated and resolved within 2 hours posttreatment. In contrast, both patients treated at the 550-mg/m2 dose level experienced a dose-limiting constellation of perinfusional aphasia and vertigo, with either ataxia of over 2 weeks' duration or recurrent dizziness. Prolongation of the infusion duration to 3 hours at this dose level resulted in less neurotoxicity; however, delayed trilineage hematologic toxicity precluded timely administration on this schedule. A statistically significant relationship was demonstrated between the development of ataxia and maximum plasma concentrations of penclomedine. CONCLUSION: Neurotoxicity was the dose-limiting toxicity (DLT) of penclomedine administered as a 1-hour infusion daily for 5 days every 3 weeks, and the recommended dose for further evaluations was 415 mg/m2. The nature of the principal toxicities and the lack of any detectible antitumor activity indicate that phase II evaluations of penclomedine on this administration schedule should be focused on specific disease settings, such as breast cancer and intracerebral tumors, in which antitumor activity has been demonstrated.     

Cytotoxic and antitumor activity of a recombinant tumor necrosis factor-B1(Fv) fusion protein on LeY antigen-expressing human cancer cells

We have constructed a fusion protein composed of tumor necrosis factor alpha (TNF-alpha) fused at its COOH terminus to the scFv region of monoclonal antibody (mAb) B1, an antibody that recognizes LeY antigen present on many human cancer cells. Our rationale for fusing the scFv to the COOH terminus of TNF was to diminish the binding of the fusion protein to TNF receptors because the COOH terminus of TNF is involved in binding, and thus to partially inactivate (detoxify) the molecule. The Fv region should then target and accumulate the fusion protein on cancer cells, which should compensate for the reduced binding affinity of the TNF moiety and lead to selective killing of TNF-sensitive antigen-expressing cancer cells. The fusion protein was expressed in Escherichia coli and found in insoluble inclusion bodies. After refolding and purification by anion exchange, Ni-NTA affinity, and size-exclusion chromatography, we obtained monomeric TNF-B1(Fv). This molecule binds to LeY antigen on cancer cells with the same affinity as B1(scFv) and B1(scFv) immunotoxins but with significantly lower affinity to the TNF receptor compared to the TNF trimer. TNF-B1(Fv) is very toxic to LeY antigen-expressing cancer cells that are sensitive to TNF (e.g., MCF-7 breast or CRL-1739 gastric cancer cells). This cytotoxicity is antibody targeted and TNF mediated because it can be prevented (as shown on MCF-7 cells) by an antibody competing for LeY antigen binding and by an antibody that neutralizes TNF-alpha. TNF-B1(Fv) kills TNF-alpha-sensitive cells that do not express the target antigen only at much higher doses than TNF trimer, and it does not kill LeY-bearing but TNF-alpha-resistant cells. TNF-B1(Fv) can cause significant tumor regression of MCF-7 tumor xenografts in mice at doses that are not toxic to the mice. Thus, the reduced binding of the TNF moiety to TNF receptors, combined with binding of the B1(Fv) portion to LeY antigen, makes TNF-B1(Fv) an agent for selective killing of LeY-expressing TNF-sensitive cancer cells.     

2-Chloroethyl-3-sarcosinamide-1-nitrosourea, a novel chloroethylnitrosourea analogue with enhanced antitumor activity against human glioma xenografts

Nitrosoureas are among the most widely used agents used in the treatment of malignant gliomas. Here, the activity of 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) was compared with that of 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU), in vivo against s.c. implanted SF-295 and U-251 central nervous system (CNS) tumor xenografts. When given i.v., q4d for 3 doses, to athymic mice bearing s.c. SF-295 tumors, SarCNU, at an optimum of 167 mg/kg/dose, produced 9 tumor-free animals of 10 total animals, 1 regression, and no evidence of overt toxicity (> or =20% body weight loss). With a similar dosing schedule, BCNU produced no tumor-free animals, six regressions, and one drug-related death at its optimum of 30 mg/kg/dose. Furthermore, SarCNU retained high antitumor activity at two lower dose levels, 66 and 45% of the optimal dose, whereas BCNU demonstrated a progressive loss of antitumor activity at lower doses. Following p.o. administration, SarCNU similarly demonstrated antitumor activity that was superior to that of BCNU. In the U-251 CNS tumor model, SarCNU yielded six of six tumor-free animals at 80 mg/kg/dose with i.p. administration q.d. for 5 days, starting on day 14, whereas BCNU, at 9 mg/kg/dose, yielded three of six tumor-free mice and one drug-related death. Again, SarCNU resulted in tumor-free animals at 66 and 45% of its optimal dose and was relatively nontoxic, in contrast to BCNU. Results of testing to date indicate that SarCNU is clearly more effective than BCNU against the human CNS tumors SF-295 and U-251 in vivo. These results encourage the initiation of clinical trials for SarCNU, in an effort to improve therapeutic approaches to glioma, but clinical trials must determine whether superiority of SarCNU in preclinical models can be extrapolated to patients.     

DNA-Directed alkylating agents. 7. Synthesis, DNA interaction, and antitumor activity of bis(hydroxymethyl)- and bis(carbamate)-substituted pyrrolizines and imidazoles

A series of bis(hydroxymethyl)-substituted imidazoles, thioimidazoles, and pyrrolizines and related bis(carbamates), linked to either 9-anilinoacridine (intercalating) or 4-(4-quinolinylamino)benzamide (minor groove binding) carriers, were synthesized and evaluated for sequence-specific DNA alkylation and cytotoxicity. The imidazole and thioimidazole analogues were prepared by initial synthesis of [(4-aminophenyl)alkyl]imidazole-, thioimidazole-, or pyrrolizine dicarboxylates, coupling of these with the desired carrier, and reduction to give the required bis(hydroxymethyl) alkylating moiety. The pyrrolizines were the most reactive alkylators, followed by the thioimidazoles, while the imidazoles were unreactive. The pyrrolizines and some of the thioimidazoles cross-linked DNA, as measured by agarose gel electrophoresis. Strand cleavage assays showed that none of the compounds reacted at purine N7 or N3 sites in the gpt region of the plasmid gpt2Eco, but the polymerase stop assay showed patterns of G-alkylation in C-rich regions. The corresponding thioimidazole bis(carbamates) were more selective than the bis(hydroxymethyl) pyrrolizines, with high-intensity bands at 5'-NCCN, 5'-NGCN and 5'-NCGN sequences in the PCR stopping assay ( indicates block sites). The data suggest that these targeted compounds, like the known thioimidazole bis(carbamate) carmethizole, alkylate exclusively at guanine residues via the 2-amino group, with little or no alkylation at N3 and N7 guanine or adenine sites. The cytotoxicities of the compounds correlated broadly with their reactivities, with the bis(hydroxymethyl)imidazoles being the least cytotoxic (IC50s >1 microM; P388 leukemia) and with the intercalator-linked analogues being more cytotoxic than the corresponding minor-groove-targeted ones. This was true also for the more reactive thioimidazole bis(carbamates) (IC50s 0.8 and 11 microM, respectively), but both were more active than the analogous "untargeted" carmethizole (IC50 20 microM). The bis(hydroxymethyl)pyrrolizine analogues were the most cytotoxic, with IC50s as low as 0.03 microM.     

Determination of PNU 153429, a new polysulphonated derivative of distamycin A, in rat plasma by reversed-phase ion-pair high-performance liquid chromatography with ultraviolet detection

A rapid and selective ion-pair high-performance liquid chromatographic (HPLC) method for the determination of 2,2'-(carbonylbis(imino-N-methyl-4,2-pyrrole carbonylimino (N-methyl-4,2-pyrrole)carbonylimino)) -bis(1,5-naphtalenedisulphonic acid), tetrasodium salt (PNU 153429,I) in rat plasma has been developed. I is a new drug currently under investigation for the treatment of rheumatoid arthritis. Aliquots of 100 microliters of plasma spiked with 10 microliters of internal standard solution (PNU 145156E, I.S.) were added to 100 microliters of acetonitrile and vortex mixed. After centrifugation, diluted aliquots of the supernatant were transferred to autosampler vials and analyzed by reversed-phase ion-pair liquid chromatography under isocratic conditions. The retention times of I.S. and I were approximately equal to 8 and 12 min, respectively. Quantitation was achieved by ultraviolet detection at 323 nm. The assay had a limit of quantitation of 0.1 micrograms ml-1 when 100 microliters of plasma were analyzed. The linearity, precision and accuracy of the method were evaluated. No interference from blank rat, mouse, dog, monkey and human plasma was observed. The suitability of the method for in vivo samples was checked by analysis of plasma samples drawn from three cannulated male rats that had received a single 100 mg kg-1 i.v. dose of the test compound.     

A novel trans-platinum coordination complex possessing in vitro and in vivo antitumor activity

As part of a drug discovery program to discover more effective platinum-based anticancer drugs, a series of platinum complexes of trans coordination geometry centered on trans-ammine(cyclohexylaminedichlorodihydroxo)platinum(IV) (JM335) has been evaluated in vitro against a panel of cisplatin-sensitive and cisplatin-resistant human tumor cell lines (predominantly ovarian). In vitro, against 5 human ovarian carcinoma cell lines, JM335 was comparably cytotoxic to cisplatin itself and over 50-fold more potent than transplatin (mean 50% inhibitory concentrations: JM335, 3.1 microM; cisplatin, 4.1 microM; transplatin, 162 microM). With the use of seven pairs of human tumor cell lines (parent and subline with acquired resistance to cisplatin and encompassing all of the known major mechanisms of resistance to cisplatin) JM335 exhibited a different cross-resistance pattern to that of its cis isomer (JM149). JM335 showed non-cross-resistance in six of the seven resistant lines, cross-resistance in the A2780cisR line possibly being associated with high levels of glutathione. Preliminary intracellular DNA binding studies showed that in contrast to transplatin, JM335 was efficient at forming DNA-DNA interstrand cross-links. In vivo, JM335 produced growth delays in excess of 15 days against 4 of 6 human ovarian carcinoma xenografts and was unique among the complexes studied in retaining some efficacy against a cisplatin-resistant subline of the murine ADJ/PC6 plasmacytoma. JM335 is the first trans-platinum complex to demonstrate marked antitumor efficacy against both murine and human s.c. tumor models and represents a significant structural lead to complexes capable of circumventing cross-resistance to cisplatin.     

Selective cardiodepressant activity of fluodipine, a fluorenone-1,4-dihydropyridine derivative

The effect of the dihydropyridine derivative, 1,4-dihydro-2,6-dimethyl-4-(fluorenon-4-yl)pyridine-3,5-dicarboxyl ic acid diallyl ester (fluodipine) was studied in vitro in different rabbit, rat and guinea pig preparations and in vivo in the rabbit in order to characterize its pharmacological profile at cardiac and at vascular sites. Compared to nifedipine, fluodipine showed a similar cardiodepressant activity, and a much lower inhibitory activity on vascular contraction. The highest tissue selectivity was observed in guinea pig preparations: fluodipine was about 2-3 times more effective than nifedipine on chronotropism and inotropism in isolated atria, and about 150 times less effective on aortic strip contraction. Accordingly, fluodipine (i) showed high-affinity binding to guinea pig ventricular L-type cardiac Ca2+ channels (Ki=2.57 nM), (ii) was about 80 times less effective than nifedipine to inhibit Ca2+ influx in vascular smooth muscle cells and (iii) induced a significant reduction of heart rate in the anesthetized rabbit (ID25=8.5 mg kg(-1), i.v.) without affecting the blood pressure up to 20 mg kg(-1), whereas nifedipine showed a significant hypotensive effect at very low doses (ID25=0.18 mg kg(-1), i.v.). The pacemaker current If of rabbit sino-atrial node myocytes was not affected by fluodipine. These findings demonstrate that fluodipine exerts selective cardiodepressant activity, likely due to a higher affinity for cardiac than for vascular Ca2+ channels.