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PubMed1992

Activity of RP 59500, a new parenteral semisynthetic streptogramin, against staphylococci with various mechanisms of resistance to macrolide-lincosamide-streptogramin antibiotics.

RP 59500 is a semisynthetic streptogramin (Sg) composed of two synergic components: RP 57669 and RP 54476. The activities of RP 59500, RP 57669 and RP 54476 were tested against 20 strains of staphylococci susceptible to macrolide, lincosamide and streptogramin antibiotics (MLS) and against strains exhibiting different MLS resistance mechanisms. RP 59500 was active against 14 strains harbouring emrA or ermC genes which were inducibly or constitutively resistant to erythromycin (MICs of 0.5-2 mg/L). Neither RP 59500, RP 57669 nor RP 54476 induced MLSB resistance. Constitutive mutants appeared at frequencies of 10(-7)-10(-8) when two MLSB-inducible strains of staphylococci were exposed to 40 mg/L each of clindamycin and RP 57669. No such mutants appeared on plates containing RP 59500 or RP 54476. The emergence of mutants was prevented if the cultures were exposed to RP 54476 (40 mg/L), indicating that such mutants are unlikely to be selected in vivo by RP 59500. However, for some constitutive mutants, MBCs of RP 59500 were as high as 8 mg/L. Strains producing acetyltransferase and hydrolase, inactivating SgA- and SgB-type antibiotics respectively, were resistant to RP 59500, RP 57669 and RP 54476. Production of Pincosamide nucleotidyltransferase-4, which inactivates lincosamides, had no effect on the MICs of RP 59500, RP 57669 and RP 54476.

Anti-Bacterial Agents↗
PubMed1993

Radiosensitization by a new potent nucleoside analog: 1-(1',3',4'-trihydroxy-2'-butoxy)methyl-2-nitroimidazole(RP-343).

PURPOSE: A new hypoxic cell sensitizer has been synthesized; this is a 2-nitroimidazole nucleoside analog having erythritol as a sugar moiety at the N-1 position of the imidazole ring (RP-343). Its possibility as a potent hypoxic cell sensitizer was compared with those of RP-170 and etanidazole. METHODS AND MATERIALS: Radiosensitization was tested in two murine tumors, EMT6 using in vitro and in vivo-in vitro assays and SCCVII using growth delay and TCD50 assays. Pharmacokinetic study was performed in Balb/c mice bearing EMT6 tumors and in Beagle dogs. LD50 of each sensitizer was obtained with ICR mice. RESULTS: As might be expected from the almost identical electron affinities of the three sensitizers, they were equally effective against hypoxic EMT6 cells in vitro. While having the lowest partition coefficient (0.035), RP-343 exhibited almost equally effective distribution to tumors and sensitizing radiation activity. An intravenous (i.v.) injection of 100 mg/kg of RP-343, RP-170 and etanidazole showed an almost equal sensitizer enhancement ratio (SER) of about 1.4 to solid EMT6 tumor under in vivo-in vitro assay and a virtually equal SER of 1.33-1.44 to solid SCCVII tumor under both tumor growth delay assay and TCD50 assay. A great advantage of RP-343 over RP-170 and etanidazole is its very much lower toxicity; their LD50 in mice were > 6.0, 4.3 and 4.8 g/kg, respectively, on i.v. injection. The lower toxicity of RP-343 was supported by its lower concentrations in the brain; the RP-343 AUC for brain was 0.43 times that of RP-170. Three indices were selected to compare the three nitroimidazoles. SER at 5% LD50 doses of RP-343, RP-170 and etanidazole was 1.66, 1.59 and 1.56. At the same toxicity levels, RP-343 was found to have better sensitization of solid tumors over both etanidazole and RP-170. The maximum tumor concentration/AUC for brain (Cmax,tumor/AUCbrain) ratios for RP-343 and RP-170 were 9.62 and 3.98. CONCLUSIONS: This extremely high ratio of RP-343 could explain its lower toxicity than RP-170 or etanidazole. The therapeutic risk index defined as D1.5/LD50 (D1.5 is the sensitizer dose to obtain the SER of 1.5 in vivo) for RP-343, RP-170 and etanidazole were 0.022, 0.033 and 0.036, respectively. Especially, the effectively lower therapeutic risk index for RP-343 presents the possibility of clinical advantage over etanidazole.

Animals↗
PubMed1992

Cellular uptake and intracellular bactericidal activity of RP 59500 in murine macrophages.

RP 59500, a new antibacterial agent, is a combination of two compounds, RP 54476 and RP 57669. The uptake of radiolabelled RP 59500, i.e. a mixture containing [14C]-RP 54476 plus RP 57669 or [14C]-RP 57669 plus RP 54476, by J 774 murine macrophages was evaluated by a velocity gradient centrifugation technique. After 120 min, the ratios of cellular to extracellular concentration for RP 54476 and RP 57669 were 34 and 50, respectively. The highest intracellular accumulation of RP 59500 was observed at pH 7-7.5. RP 59500 was found to accumulate less at 4 degrees C than at 37 degrees C. The uptake of RP 59500 by dead macrophages was markedly higher than that by live macrophages. As the extracellular concentration of RP 59500 was increased, the intracellular concentration of each component rose, but not proportionally. The metabolic inhibitors sodium cyanide and potassium fluoride both decreased modestly the entry of RP 57669, but not that of RP 54476, into macrophages. After removal of the extracellular antibiotic, RP 54476 and RP 57669 were released rapidly by the cells until equilibrium was established (45% of the original intracellular RP 59500 remained in the cells after 120 min). The intracellular activity of RP 59500 was assessed by incubating macrophages containing ingested Staphylococcus aureus 209P with the drug (10 x MIC: 2.5 mg/L) at 37 degrees C and determining the number of viable cell-associated bacteria. Approximately 70% of the intracellular bacteria were killed within 120 min of incubation. Thus, RP 59500 attains a high intracellular concentration and is active against intracellular S. aureus.

Drug Combinations↗
PubMed1993

Distinct roles of cdk2 and cdc2 in RP-A phosphorylation during the cell cycle.

RP-A is a single-stranded DNA-binding protein, which has been shown to be required for DNA replication using an SV40 model system. The protein has also been shown to be phosphorylated at the G1-S phase transition. Using Xenopus cell-free extracts we have investigated the role of RP-A in nuclear replication and characterized the kinases and conditions that lead to phosphorylation of RP-A during the cell cycle. By immunodepleting RP-A from Xenopus extracts we have shown that RP-A is essential for replication of chromosomal DNA. Our results show that, during S phase, only that RP-A which is associated with nuclei is phosphorylated. Furthermore our results indicate that during S phase RP-A is only phosphorylated when associated with single-stranded DNA. By immunodepleting cdk2 kinase we show that cdk2 kinase is required for the observed phosphorylation of RP-A in nuclei during S phase. However, using purified cdk2 kinase and RP-A we are unable to detect a direct phosphorylation of RP-A by cdk2 kinase. This observation suggests that phosphorylation of DNA-bound RP-A at S phase is carried out by a kinase distinct from cdk2. Consistent with this we find that when single-stranded DNA is added to S phase extracts depleted of cdk2 kinase, RP-A is phosphorylated. Together these results suggest that cdk2 kinase participates in the activation of DNA replication at a stage prior to the binding of RP-A to the initiation complex. In addition to RP-A phosphorylation in S phase, we have also found that at the onset of mitosis RP-A is quantitatively phosphorylated and that phosphorylation is directly mediated by cdc2 kinase. However, at this time during the cell cycle, cdc2-dependent phosphorylation of RP-A is independent of DNA binding. These observations further demonstrate the distinctions between cdk2 and cdc2 kinases.

Animals↗
PubMed1994

Anti-inflammatory and bronchodilator properties of RP 73401, a novel and selective phosphodiesterase type IV inhibitor.

1. We have investigated the effects of RP 73401, a novel, potent and highly selective cyclic nucleotide phosphodiesterase (PDE) type IV inhibitor, in guinea-pig and rat models of bronchoconstriction and allergic inflammation. In some models, the effects of RP 73401 have been compared with those of the standard PDE type IV inhibitor, rolipram. 2. RP 73401 (0.4-400 micrograms kg-1, intratracheally (i.t.) on lactose) inhibited antigen-induced bronchospasm in previously sensitized conscious guinea-pigs (ID50: 7 +/- 1 micrograms kg-1) and in anaesthetized rats (ID50: 100 +/- 25 micrograms kg-1). Rolipram inhibited the antigen-induced bronchospasm in guinea-pigs with an ID50 of 5 +/- 1 micrograms kg-1. In guinea-pig bronchoalveolar lavage (BAL) fluid, total inflammatory cell and eosinophil numbers were reduced by RP 73401 (ID50s: 3.9 +/- 0.8 micrograms kg-1 and 3.2 +/- 0.7 micrograms kg-1, respectively). In the rat, inflammatory cell numbers are less affected. Only the highest dose of RP 73401 (400 micrograms kg-1) significantly inhibited eosinophil influx (41 +/- 16% inhibition). 3. RP 73401 (0.02-100 micrograms kg-1, i.v.) inhibited PAF-induced bronchial hyperreactivity to bombesin in the anaesthetized guinea-pig (ID50: 0.09 +/- 0.03 micrograms kg-1) and inhibited (0.4-40 micrograms kg-1, i.t.) histamine-induced airway microvascular leakage in the anaesthetized guinea-pig by approximately 60% at all doses. 4. RP 73401 relaxed guinea-pig isolated trachea under basal tone (EC50: 9 nM) and when precontracted with histamine (IC50: 2 nM), methacholine (IC50: 29 nM) or leukotriene D4 (LTD4, IC50: 4 nM). 5. RP 73401 (0.4-100 microg kg-1, i.t.) inhibited bronchospasm induced by histamine (ID.%: 34 +/- 6 microg kg-1), methacholine (ID50: 66 +/- 12 pg kg-1) and LTD4 (ID50: <4 microg kg-1) in the anaesthetized guinea pig.Against these same bronchoconstrictors, rolipram (i.t.) had ID5o values of 44 +/- 4, 72 +/- 18 and<4 pg kg- respectively. RP 73401 (4 and 40 pg kg-, i.t.) increased the magnitude and duration of bronchodilatation produced by salbutamol in the anaesthetized guinea-pig. At doses producing significant bronchodilatation, RP 73401 was without effect on heart rate or blood pressure in the anaesthetized guinea-pig. RP 73401 (0.01 -0.25 mg kg-1, i.v.) did not affect heart rate and produced only a small fall in blood pressure in the anaesthetized rat.6. These data demonstrate that RP 73401 and rolipram inhibit antigen- and mediator-induced bronchospasmin guinea-pigs with the same potency. Furthermore, RP 73401 administered directly into the airways, protects against allergic airway inflammation. These results indicate the importance of PDE IV in regulating smooth muscle and inflammatory cell activity. At doses suppressing the inflammatory response in the lung, RP 73401 had little effect in the cardiovascular system. RP 73401 may have a role as a bronchodilator and, more importantly, as a prophylactic anti-inflammatory agent in the treatment of asthma.

Albuterol↗
PubMed1994

Effects of RP 67580, a tachykinin NK1 receptor antagonist, on a primary afferent-evoked response of ventral roots in the neonatal rat spinal cord.

1. The pharmacological characteristics of RP 67580, a non-peptide tachykinin NK1 receptor antagonist, and its effects on a reflex response evoked by stimulation of primary afferent fibres, were examined in isolated neonatal spinal cord preparations of the rat. Potentials were recorded extracellularly from a lumbar ventral root and drugs were bath-applied in normal artificial cerebrospinal fluid (CSF) or in the presence of tetrodotoxin (TTX). 2. In normal artificial CSF, RP 67580 (0.1-0.3 microM) caused rightward shifts of the concentration-response curves for substance P (SP), neurokinin A (NKA) and substance P methyl ester (SPOMe), an NK1-selective agonist, with pA2 values of 7.25, 7.47 and 7.49, respectively. 3. In the presence of TTX (0.3 microM), RP 67580 also caused rightward shifts of the concentration-response curves for SPOMe and NKA. The pA2 value of RP 67580 against SPOMe (6.75) was significantly lower than that against NKA (7.22). RP 67580 (0.3-1 microM) did not cause a clear parallel shift of the concentration-response curves for SP, and it depressed the depolarizations induced by low concentrations of SP, but slightly potentiated those induced by high concentrations of SP. 4. RP 67580 (1 microM) did not depress the depolarizing responses to bombesin, L--glutamate, gamma-aminobutyric acid (GABA), thyrotropin-releasing hormone and muscarine. RP 67580 (1 microM), however, depressed the response to acetylcholine in the presence of atropine and the response to nicotine. RP 68651 (1 microM), the enantiomer of RP 67580 devoid of activity at tachykinin NK1 receptors, also depressed the response to acetylcholine in the presence of atropine. 5. RP 67580 (1 gAM) did not induce GABA release from the rat spinal cord.6. In the neonatal gerbil spinal cord, the antagonist effects of RP 67580 (0.3-1 JAM) against SPOMe were much less potent than in the neonatal rat spinal cord.7. In the rat spinal cord-saphenous nerve preparation, electrical stimulation of the saphenous nerve atC-fibre strength evoked a prolonged depolarization of the ipsilateral L3 ventral root (slow VRP).RP 67580 (0.1-1 JM) depressed the saphenous nerve-evoked slow VRP. In contrast, RP 68651 (0.3 JAM)had no effect on the slow VRP.8. The results of the present study indicate that RP67580 acts as a high affinity NK, receptor antagonist in the neonatal rat spinal cord, although it also possesses an antinicotinic action. This study further suggests the existence of a subpopulation of tachykinin NK, receptors that are activated by NKA and SPOMe, as well as by low concentrations of SP, and are sensitive to the antagonist action of RP 67580 in the neonatal rat spinal cord. This study also provides further evidence for the involvement of SP and NKA in the slow VRP evoked by C-fibre stimulation in the neonatal rat spinal cord.

Animals↗
PubMed1996

Antipneumococcal activities of RP 59500 (quinupristin-dalfopristin), penicillin G, erythromycin, and sparfloxacin determined by MIC and rapid time-kill methodologies.

Previous time-kill studies have shown that RP 59500 is rapidly bactericidal against pneumococci. To extend these findings, the activities of RP 59500, its two components RP 57669 RP 54476, penicillin G, erythromycin and sparfloxacin against 26 penicillin-susceptible, 25 penicillin-intermediate, and 25 penicillin-intermediate, and 25 penicillin-resistant pneumococci were determined by the agar dilution MIC and the time-kill testing methodologies within 10 min (ca. 0.2 h) and at 1 and 2 h. Respective agar dilution MICs at which 90% of isolates are inhibited for penicillin-susceptible, -intermediate, and -resistant strains were as follows: penicillin G, 0.03, 1, and 4 micrograms/ml;RP 59500, 1, 1, and 1 microgram/ml; RP 57669, 8, 32, and 16 micrograms/ml; RP 54476, > 128, > 128, and > 128 micrograms/ml; erythromycin, 0.06, 2, and > 128 micrograms/ml; and sparfloxacin, 1, 0.5, and 0.5 microgram/ml. RP 59500 was equally active (MIC at which 90% of isolates are inhibited, 1.0 microgram/ml) against erythromycin-susceptible and -resistant strains. Time-kill testing results showed that only RP 59500 at one to four times the MIC killed pneumococci at 0.2 h; RP 59500 was also the most active compound at 1 and 2 h. By comparison, penicillin and sparfloxacin at one, two, and four times the MICs reduced the original inoculum by > or = 1 log at 2 h for 46, 80, and 95% and for 50, 72, and 86% of strains, respectively. The killing activity of RP 59500 was the same against erythromycin-susceptible and -resistant strains. RP 57669, RP 54479, and erythromycin were either inactive or bacteriostatic at 2 h. Of all drugs tested, RP 59500 yielded the most rapid killing.

Anti-Bacterial Agents↗
PubMedDate not supplied

Parathyroid hormone-related peptide (PTH-rp) in normal, hyperplastic and malignant endometrial tissue: an immunohistochemical analysis.

UNLABELLED: Parathyroid hormone-related peptide (PTH-rp) is a peptide initially purified from tumors with hypercalcemia, which is also produced in human endometrium. The aim of this study was to determine the frequency and tissue distribution of PTH-rp in normal, hyperplastic and malignant endometrium. MATERIALS AND METHODS: Paraffin-fixed endometrial tissue was obtained randomly from women in the proliferative (n = 4), early secretory (n =5) and late secretory (n = 5) phases, as well as glandular-cystic hyperplasia (n = 5), adenomatous hyperplasia (AH) grade I (n = 5), grade II (n = 4), grade III (n = 4) and endometrioid adenocarcinoma grade I (n = 5). The PTH-rp expression was evaluated by immunohistochemical procedure. A semiquantitative analysis and a statistical evaluation was performed. RESULTS: Immunohistochemical reaction with PTH-rp was primarily observed in glandular and luminal epithelial cells. Stromal and myometrial cells also expressed PTH-rp. The expression of PTH-rp in glands was significantly higher during the late secretory than in the proliferative phase. The highest expression was observed during AH grade III, while the lowest reaction was detected in the proliferative phase and adenocarcinoma. DISCUSSION: PTH-rp was expressed in normal, hyperplastic and malignant endometrial tissue. A cyclical expression of PTH-rp in normal glandular epithelium was observed, being more prominent in the late secretory phase. AH grade I to III also expressed PTH-rp with higher immunostaining than adenocarcinoma. Since AH grade III can be considered as a precursor of endometrial cancer, PTH-rp could be a marker of cell transformation. Endometrioid adenocarcinoma expressed the lowest PTH-rp immunostaining, indicating either a lower expression or a reflection of an increased PTH-rp shedding of malignant transformed endometrium. Further studies are required to establish the usefuleness of PTM-rp as a marker in different endometrial pathologies.

Endometrial Hyperplasia↗
PubMed1997

[Comparative antimicrobial activity of RP 59,500 (quinupristin-dalfopristin), the first semisynthetic injectable streptgramin, against gram-positive cocci and other recent clinical pathogens].

RP 59,500 (Quinupristin-Dalfopristin) is the first semisynthetic injectable streptogramin antimicrobial agent, which is a combination of quinupristin and dalfopristin in a 30:70 ratio. The components of RP 59,500 act synergically to provide bactericidal activity through action at different sites on bacterial ribosomes. In the present study, the antimicrobial activity of RP 59,500 was compared with those of four macrolides (erythromycin, clarithromycin, azithromycin, roxithromycin). Susceptibility testing was carried out by microdilution method on 303 strains of 10 species, especially antibiotic-resistant Gram-positive cocci. RP 59,500 was active against a wide range of Gram-positive cocci including methicillin-resistant Staphylococci and penicillin-resistant Streptococcus pneumoniae. The MICs90 of RP 59,500 against methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis were both 0.25 microgram/ml, although those of four macrolides were higher than 32 micrograms/ml. The MICs90 of RP 59,500 against penicillin-sensitive, -intermediate and -resistant S. pneumoniae were all 0.5 microgram/ml, although those of four macrolides against penicillin-resistant S. pneumoniae were higher than 32 micrograms/ml. RP 59,500 also exhibited equivalent activities to the four macrolides against strains of Streptococcus pyogenes. Streptococcus agalactiae and Moraxella catarrhalis. RP 59,500 exhibited the highest activities against Enterococcus faecalis, Enterococcus faecium and Enterococcus avium strains which are intrinsically resistant to most antimicrobial agents. No cross-resistance was observed between RP 59,500 and the four macrolides, which will merit attention in future clinical trials of the agent. The effect of human serum on the MIC of RP 59,500 was studied with strains of S. aureus, S. epidermidis and E. faecalis. The presence of 20% (V/V) serum had little or no effect on the MIC, although 50% (V/V) serum increased MICs by 4-8 folds. Laboratory-induced resistance to RP 59,500 occurred in a stepwise fashion in broth cultures of S. aureus, S. epidermidis and E. facalis strains and the induction rate was slow and no more than four fold increases were observed. Population analysis was performed on RP 59,500 and the reference macrolides against S. aureus ATCC 25,923 strain. Although low frequencies (less than 0.01%) of resistant sub-population were detected with EM, CAM, AZM and RXM, no RP 59,500-resistant sub-population was detected in this study.

Anti-Bacterial Agents↗
PubMed1998

Effect of the platelet-activating factor antagonist RP 59227 (Tulopafant) on myocardial ischemia/reperfusion injury and neutrophil function.

The effect of the platelet activating factor antagonist RP 59227 (Tulopafant) on myocardial infarct size was compared to that of a vehicle-treated control group in barbital-anesthetized dogs subjected to 90 min of left circumflex coronary artery occlusion and 5 h of reperfusion. The myocardial region at risk and infarct size were determined by the triphenyltetrazolium histochemical technique and regional myocardial blood flow by radioactive microspheres. Myeloperoxidase (MPO) activity was used as an index of neutrophil infiltration into the ischemic-reperfused area. Vehicle (n = 11) or RP 59227 (n = 12, 2.5 mg/kg i.v.) were administered 15 min prior to occlusion. Hemodynamics and regional myocardial blood flow in the ischemic-reperfused areas did not differ between the two groups throughout the experiment. In contrast, the number of dogs which developed ventricular fibrillation during occlusion and reperfusion was significantly less in RP 59227-treated dogs (8 of 11 in the control group vs. 3 of 12 in the RP 59227-treated group, p < 0.05). Myocardial infarct size expressed as a percent of the area at risk (control, 39.0 +/- 5.0; RP 59227, 24.8 +/- 3.4%) or as a percent of the left ventricle (control, 15.3 +/- 1.9; RP 59227, 9.0 +/- 1.3%) was significantly smaller in the RP 59227-treated group. Infarct size was inversely related to the collateral blood flow in the inner two thirds of the left ventricular wall of the infarct area, and this relationship was shifted downward in the RP 59227-treated group (p < 0.05). MPO activity in the border zone immediately adjacent to infarcted tissue was reduced in the RP 59227-treated dogs (control, 7.4 +/- 0.5 U/g; RP 59227, 4.1 +/- 0.4 U/g). In additional in vitro studies, the addition of PAF was found to elicit a concentration-dependent potentiation in chemiluminescence produced by purified canine neutrophils, a measure of oxygen-derived free radicals, which was stimulated with a low concentration of opsonized zymosan. Preincubation of neutrophils with RP 59227 resulted in a concentration-dependent decrease in chemiluminescence produced by PAF primed cells. Taken together, these data demonstrate that RP 59227 effectively reduces myocardial infarct size and reduces the incidence of ischemia and reperfusion-induced arrhythmias in barbital-anesthetized dogs, and support the concept that PAF plays an important role in the pathogenesis of acute myocardial infarction.

Animals↗
PubMed1987

PAF binding sites. Characterization by [3H]52770 RP, a pyrrolo[1,2-c]thiazole derivative, in rabbit platelets.

52770 RP, the N-(3-chlorophenyl)-3-(3-pyridinyl)-1H,3H-pyrrolo[1,2-c]thiazole -7-carboxamide, displaces in a potent, specific and competitive manner [3H]PAF from its binding sites on rabbit platelets. Since 52770 RP is not structurally related to PAF and has low liposolubility with respect to PAF, it was selected as a potential radioligand for PAF receptor sites. [3H]52770 RP displayed high-affinity, specificity, as well as saturable and displaceable binding to a single class of recognition sites in intact platelets and crude platelet membranes. In these preparations, the values of binding parameters were, respectively, 8.5 and 7.6 nM for Kd, 0.2 pmol/5 X 10(7) platelets and 3.66 pmol/mg protein for Bmax and 0.96 and 0.91 for nH. Inasmuch as the (+)-52770 RP was 300-fold more potent than the (-)-isomer at displacing [3H]52770 RP in intact platelets, the studied binding site manifested stereospecific discrimination. A variety of pharmacological agents including pro- and anti-aggregant compounds did not exhibit affinity for [3H]52770 RP binding sites. In contrast, PAF, some of its active analogues and several recognized PAF antagonists (BN 52021, brotizolam, L-652,731, triazolam), displaced the [3H]52770 RP binding. Studies carried out using [3H]PAF demonstrated that 52770 RP was approximately 4- and 200-fold more potent than L-652,731 and BN 52021 respectively, as a PAF-receptor antagonist. In washed rabbit platelets, the rank order of potency (Ki) for several analogues of 52770 RP, to displace [3H]PAF from its binding sites, was highly correlated (r = 0.96) to their ability to antagonize [3H]52770 RP binding. In functional studies, 52770 RP antagonized not only the PAF-induced aggregation in washed rabbit platelets but also the hypotension evoked by PAF in the anesthetized rat. In this respect, it was 26 and 2 times more potent than L-652,731, respectively. In conclusion, [3H]52770 RP might represent a novel interesting tool for furthering our understanding of the role of PAF binding sites in pathophysiological processes.

Animals↗
PubMed1995

Suppression of eosinophil function by RP 73401, a potent and selective inhibitor of cyclic AMP-specific phosphodiesterase: comparison with rolipram.

1. We have investigated the inhibitory potency of RP 73401, a novel, highly selective and potent inhibitor of cyclic AMP-specific phosphodiesterase (PDE IV), against partially-purified PDE isoenzymes from smooth muscle and the particulate PDE IV from guinea-pig eosinophils. The inhibitory effects of RP 73401 on the generation of superoxide (.O2-), major basic protein (MBP) and eosinophil cationic protein (ECP) from guinea-pig eosinophils have also been studied. 2. RP 73401 potently inhibited partially-purified cyclic AMP-specific phosphodiesterase (PDE IV) from pig aortic smooth muscle (IC50 = 1.2 nM); it was similarly potent against the particulate PDE IV from guinea-pig peritoneal eosinophils (IC50 = 0.7 nM). It displayed at least a 19000 fold selectivity for PDE IV compared to its potencies against other PDE isoenzymes. Rolipram was approximately 2600 fold less potent than RP 73401 against pig aortic smooth muscle PDE IV (IC50 = 3162 nM) and about 250 times less potent against eosinophil PDE IV (IC50 = 186 nM). 3. Solubilization of the eosinophil particulate PDE IV increased the potency of rolipram 10 fold but did not markedly affect the potency of RP 73401. A similar (10 fold) increase in the PDE IV inhibitory potency of rolipram, but not RP 73401, was observed when eosinophil membranes were exposed to vanadate/glutathione complex (V/GSH). 4. Reverse transcription polymerase chain reaction (RT-PCR), using primer pairs designed against specific sequences in four distinct rat PDE IV subtype cDNA clones (PDE IVA-D), showed only mRNA for PDE IVD in guinea-pig eosinophils. PDE IVD was also the predominant subtype expressed in pig aortic smooth muscle cells. 5. RP 73401 (Kiapp = 0.4 nM) was 4 fold more potent than (+/-)-rolipram (Kiapp = 1.7 nM) in displacing[3H]-(+/-)-rolipram from guinea-pig brain membranes.6. In intact eosinophils, RP 73401 potentiated isoprenaline-induced cyclic AMP accumulation(EC50 = 79 nM). RP 73401 also inhibited leukotriene B4-induced generation of *02- (IC50 = 25 nM), and the release of major basic protein (ICo = 115 nM) and eosinophil cationic protein (IC50 = 7 nM). Rolipram was 3-14 times less potent than RP 73401.7. Thus RP 73401 is a very potent and selective PDE IV inhibitor which suppresses eosinophil function suggesting that it may be a useful agent for the treatment of inflammatory diseases such as asthma. The greatly different inhibitory potencies of rolipram against PDE IV from smooth muscle and eosinophils(in contrast to the invariable effects of RP 73401) are unlikely to be attributable to diverse PDE IV subtypes but suggest distinct interactions of the two inhibitors with the enzyme.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1994

Significance of plasma PTH-rp in patients with hypercalcemia of malignancy treated with bisphosphonate.

BACKGROUND: Hypercalcemia of malignancy (HM) is one of the commonest metabolic complications associated with cancer. Plasma parathyroid hormone-related peptide (PTH-rp) is known to cause hypercalcemia in the vast majority of patients with HM. METHODS: Fifty-two patients with HM were treated with a single infusion of 60 mg of pamidronate (3-amino-1-hydroxypropylidene-1, 1-bisphosphonate). Serum calcium and plasma PTH-rp levels were measured at the basal and after pamidronate therapy. RESULTS: Normocalcemia was achieved in 43 (i.e., 83%) of these patients within 3 to 5 days. Eighty-one percent had increased plasma PTH-rp levels. There was no difference in the percentages of patients who had elevated plasma PTH-rp levels compared with those of patients with metastatic bone disease and humoral HM. However, the latter group of patients had significantly higher circulatory PTH-rp levels (P < 0.01). The pretreatment calcium levels were not correlated with the calcium-lowering responses nor with plasma PTH-rp levels. However, there was a significant positive correlation between pretreatment plasma PTH-rp levels and the nadir serum calcium (P < 0.001) and a negative correlation with the changes in serum calcium levels (P < 0.001) after pamidronate therapy. No relationship existed between pretreatment calcium levels or PTH-rp levels with the extent or the severity of the metastatic bone disease. Patients who had the highest PTH-rp levels had the worst prognosis, poorest calcium-lowering effect, shortest duration of normocalcemia, and required higher doses and frequent infusions of pamidronate to maintain normocalcemia. The nonresponders to therapy had a significantly higher mean plasma PTH-rp level (> 75 pg/ml) than the responders (P < 0.01). CONCLUSIONS: The plasma PTH-rp levels may help to predict the calcium-lowering effect of bisphosphonate and give an indication of the prognosis in patients with HM. They may allow identification of patients who need higher doses and increased frequency of administration of bisphosphonate, thereby expediting the normocalcemic response.

Adult↗