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Thrombosis Research Jul 1986Adenosine (Ado, 10-50 microM), a potent inhibitor of ADP-induced human platelet aggregation in platelet-rich plasma (PRP), does not inhibit aggregation in whole blood....
Adenosine (Ado, 10-50 microM), a potent inhibitor of ADP-induced human platelet aggregation in platelet-rich plasma (PRP), does not inhibit aggregation in whole blood. However, the Ado analogs, 2-fluoroadenosine, 2-chloroadenosine and 5'-N-ethylcarboxamidoadenosine (NECA) which are resistant to deamination (2-fluoroadenosine) or deamination and phosphorylation (2-chloroadenosine and NECA), inhibit aggregation in whole blood with IC50 values of 12 microM, 2.3 microM and 0.26 microM, respectively. The inhibitory effect of NECA (200 nM) is potentiated by the platelet cAMP phosphodiesterase (PDE) inhibitor RA 233 (5 microM). Inhibition of the erythrocytic nucleoside transport system by dilazep (1 microM) or dipyridamole (10 microM), or blockade of Ado metabolism by 2'-deoxycoformycin (5 microM) plus 5-iodotubercidin (10 microM), evokes the antiaggregatory action of Ado in whole blood (IC50 congruent to 2 microM). RA 233 (5 microM) potentiates Ado-mediated inhibition about 10-fold when nucleoside transport or Ado metabolism is blocked. Ado (10 microM or 200 nM) is rapidly metabolized within 1 min in whole blood. When nucleoside transport is inhibited by dilazep or dipyridamole, or when Ado metabolism is blocked by 2'-deoxycoformycin and 5-iodotubercidin, 50-60% of the Ado remains in the plasma after 5 min. These results show that the failure of Ado to inhibit platelet aggregation in whole blood results from its rapid uptake and metabolism by erythrocytes. More importantly, these data emphasize the key role of nucleoside transport inhibition in the antiplatelet actions of dipyridamole and dilazep. In addition, superior therapeutic results may be obtained from the combination of blockade of nucleoside transport system with inhibition of platelet cAMP PDE.
Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Adenosine; Azepines; Biological Transport, Active; Blood Platelets; Cyclic AMP; Dilazep; Dipyridamole; Drug Synergism; Humans; In Vitro Techniques; Mopidamol; Nucleosides; Platelet Aggregation; Pyrimidines
PubMed: 3016942
DOI: 10.1016/0049-3848(86)90057-5 -
Archives of Neurology May 1981In an investigation of the role of platelets in vasogenic edema in cats, direct observation of the cortex revealed that within several minutes after cold injury,...
In an investigation of the role of platelets in vasogenic edema in cats, direct observation of the cortex revealed that within several minutes after cold injury, platelet thrombi formed in small veins at the point where the veins emerged from the depths of the brain. Later, edema fluid extravasated from the veins at this same point. Pretreatment with a platelet inhibitor, RA-233, abolished the formation of platelet thrombi and remarkably enhanced the leakage of edema fluid. The microcirculation was assessed by carbon black perfusion and was found to fill better in the cats that received the platelet inhibitor. The better filling may be ascribed to a decreased number of thrombi and consequent improved blood flow in small blood vessels. We conclude that platelet aggregates play a major role in controlling the leakage of edema fluid after cold injury.
Topics: Animals; Blood Platelets; Brain; Brain Edema; Cats; Cerebrovascular Circulation; Intracranial Embolism and Thrombosis; Mopidamol; Platelet Adhesiveness; Platelet Aggregation
PubMed: 7224908
DOI: 10.1001/archneur.1981.00510050031002 -
European Journal of Cancer & Clinical... Sep 1987The pyrimido-pyrimidine derivatives RA 233 and RX-RA 85, which are potent inhibitors of platelet and tumor phosphodiesterase, were developed as antitumor agents. When...
The pyrimido-pyrimidine derivatives RA 233 and RX-RA 85, which are potent inhibitors of platelet and tumor phosphodiesterase, were developed as antitumor agents. When tested by us, these drugs were cytostatic at low concentrations and produced dramatic changes in cell shape and organization of cytoskeletal structures in cultured MTF7 cells derived from the rat 13762NF mammary adenocarcinoma. At high concentrations (up to 600 micrograms/ml) RA 233 was cytostatic but not cytotoxic to MTF7 cells during a 24 hr incubation in vitro, whereas RX-RA 85 was cytotoxic at concentrations above 4 micrograms/ml. These drugs caused MTF7 cells to elongate and form numerous vacuoles, which surrounded the cell nucleus. Treatment of MTF7 cells with RA 233 or RX-RA 85 enhanced microtubular organization concomitant with a decrease in microfilament organization. In contrast, treatment of MTF7 cells with 1 mM dibutyryl cAMP resulted in an enhanced organization of microtubules but had no effect on microfilament organization. Previous studies suggested that RA 233 and RX-RA 85 increase cAMP levels in 2 other cell clones of rat 13762NF mammary adenocarcinoma by inhibiting phosphodiesterases. However, additional sites of drug action should also be considered based on the effects of these drugs on microfilament systems and cell vacuoles.
Topics: Actin Cytoskeleton; Adenocarcinoma; Animals; Cell Line; Cell Survival; Cytoskeleton; Dose-Response Relationship, Drug; Mammary Neoplasms, Experimental; Microtubules; Mopidamol; Phosphodiesterase Inhibitors; Pyrimidines; Rats; Vacuoles
PubMed: 3678321
DOI: 10.1016/0277-5379(87)90107-6 -
Clinical & Experimental Metastasis Jan 1994Prostacyclin and its stable analogues have been shown to interfere specifically with certain steps of the metastatic cascade. The antimetastatic activity of the stable...
Prostacyclin and its stable analogues have been shown to interfere specifically with certain steps of the metastatic cascade. The antimetastatic activity of the stable prostacyclin analogue Cicaprost (Schering AG) on haematogenous metastasis in a series of tumours in rats and mice has been well established. In order to test the effect of Cicaprost on lymphogenous metastasis we chose the metastatic cell clone MTLn3 derived from the 13762NF rat mammary carcinoma. The effect of Cicaprost on prevention of lung metastasis, lymph node metastasis and primary tumour growth was investigated. Cicaprost given in daily doses of 0.01, 0.03 and 0.1 mg/kg orally, reduced the number of lung metastases in a dose-dependent manner. Whereas the median number of lung metastases in the controls was greater than 1000, Cicaprost at a dose of 0.1 mg/kg reduced the number of lung metastases to between 11 and 100. The weight of the ipsilateral axillary lymph nodes was diminished by Cicaprost to 30-50% of controls. Moreover, metastasis to the contralateral axillary lymph node was completely inhibited by Cicaprost at all three doses tested. Cicaprost did not influence the growth rate of the MTLn3 cell clone implanted into the mammary fat pad or the weight of the primary tumour at the end of treatment. In conclusion, in addition to its dose-dependent effect on haematogenous metastasis, Cicaprost strongly inhibits lymph node metastasis.
Topics: Animals; Antineoplastic Agents; Dose-Response Relationship, Drug; Epoprostenol; Female; Lung Neoplasms; Lymphatic Metastasis; Mammary Neoplasms, Experimental; Mopidamol; Rats; Rats, Inbred F344
PubMed: 8287616
DOI: 10.1007/BF01784330 -
Journal of Medicine 1996A series of pyrimido-pyrimidine derivatives were tested for their effect on membrane fluidity-deformability of human red blood cells and on human platelet aggregation....
A series of pyrimido-pyrimidine derivatives were tested for their effect on membrane fluidity-deformability of human red blood cells and on human platelet aggregation. These agents were also tested for their intracellular cAMP increasing activity and proliferation inhibitory activity in neoplastic cells. The order of activity was established and clinical implications discussed. Several derivatives are under study as antineoplastic agents.
Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Adenosine Diphosphate; Antineoplastic Agents; Cell Division; Cyclic AMP; Erythrocyte Deformability; Hemorheology; Humans; Melanoma; Molecular Structure; Mopidamol; Platelet Aggregation; Platelet Aggregation Inhibitors; Pyrimidines; Tumor Cells, Cultured
PubMed: 8863175
DOI: No ID Found -
Cancer Treatment Reports Nov 1987Flurbiprofen, 0.25 mg/kg, administered to mice orally once daily during 3 days prior to an iv transplantation of Lewis lung carcinoma cells, protected 50%-57% of...
Flurbiprofen, 0.25 mg/kg, administered to mice orally once daily during 3 days prior to an iv transplantation of Lewis lung carcinoma cells, protected 50%-57% of experimental animals from the formation of lung tumor colonies. With the daily dose of 1.0 mg/kg, this effect was less pronounced. Mopidamole, twice daily 90 mg/kg orally during 3 days, did not have this effect.
Topics: Administration, Oral; Animals; Antineoplastic Combined Chemotherapy Protocols; Flurbiprofen; Lung Neoplasms; Male; Mice; Mice, Inbred C57BL; Mopidamol; Neoplasm Transplantation; Propionates; Pyrimidines
PubMed: 3677114
DOI: No ID Found -
Journal of Cellular Physiology Nov 1988RA 233, a pyrimido-pyrimidine analogue developed originally as an antiplatelet agent, has reduced the incidence of tumor metastases in clinical trials. However, in...
RA 233, a pyrimido-pyrimidine analogue developed originally as an antiplatelet agent, has reduced the incidence of tumor metastases in clinical trials. However, in animal tumor models antimetastatic therapy using RA 233 has been inconsistent. We therefore tested RA 233 for additional effects, such as its direct action on tumor cells. Using the rat 13726NF mammary adenocarcinoma tumor system, low, nontoxic concentrations of RA 233 had pleiotropic and differential effects on two 13762NF tumor cell clones. The growth of MTC cells (low spontaneous metastatic potential) was not affected by low concentrations of RA 233 (50 microM) or epidermal growth factor (EGF) (up to 10 ng/ml) for 3 days in 0.5-10% fetal bovine serum. In contrast, MTLn3 (high spontaneous metastatic potential) cell cultures maintained for 3 days in low (0.5-1%) serum in the presence of 1.25-10 ng/ml EGF doubled in cell numbers compared with control cultures, and addition of 50 microM RA 233 abrogated the growth-stimulatory effect of EGF. The inhibitory effect of RA 233 on MTLn3 cells was dose dependent and not due to cell toxicity as determined by cell viability, cell growth, and colony formation properties after drug removal. In addition, incubation of MTLn3 cells with 50 microM RA 233 resulted in an increase of p21ras protein expression, whereas there was no effect on the level of p21ras in identically treated MTC cells or when either clone was treated with 10 ng/ml EGF. The results suggest that among the heterogeneous effects of RA 233 on tumor cells, modulation of growth factor responses and regulatory molecules may be important.
Topics: Adenocarcinoma; Animals; Cell Division; Epidermal Growth Factor; Mammary Neoplasms, Experimental; Mopidamol; Proto-Oncogene Proteins; Proto-Oncogene Proteins p21(ras); Pyrimidines; Rats
PubMed: 3056958
DOI: 10.1002/jcp.1041370211 -
Clinical & Experimental Metastasis 1987Possible prophylactic antitumor and/or antimetastatic effects of long-term oral administration of a potent inhibitor of platelet aggregation, the pyrimido-pyrimidine...
Possible prophylactic antitumor and/or antimetastatic effects of long-term oral administration of a potent inhibitor of platelet aggregation, the pyrimido-pyrimidine derivative RA233, were assessed using four phenotypically distinct clones of the mouse B16 melanoma. The clones tested included: a poorly tumorigenic, very slowly growing and poorly metastatic population (G3.15); a moderately tumorigenic and slowly growing population that frequently metastasizes to the lungs (G3.5); a highly tumorigenic, moderately growing and highly metastatic population (G3.12); and a highly tumorigenic and rapidly growing population that is generally nonmetastatic but can be slightly metastatic when tumors are initiated by very small numbers of cells (G3.26). Addition of 0.5 mg/ml RA233 to the drinking water continuously from the time of subcutaneous injection of cultured tumor cells until death from tumor growth, which resulted in a daily uptake of 80-100 mg/kg of drug per mouse, failed to significantly influence the tumorigenicities, tumor growth rates, metastatic incidences, or metastatic burdens of any of these clones. RA233 at doses equivalent to those delivered daily to experimental animals strongly inhibited ADP-induced aggregation of homologous C57BL/6 mouse platelets and exhibited selective anti-proliferative effects on cultured cells. Although RA233 prolonged bleeding times, pharmacokinetic analysis indicated that clearance of RA233 from mice was so rapid that achievement of sustained circulating levels sufficient to influence tumor cells or platelet-tumor cell interactions by oral administration was unlikely.
Topics: Administration, Oral; Animals; Antineoplastic Agents; Blood Platelets; Female; Melanoma; Mice; Mice, Inbred C57BL; Mopidamol; Neoplasm Metastasis; Pyrimidines
PubMed: 3594974
DOI: 10.1007/BF00058062 -
The Journal of Biological Chemistry Jan 1984The cycle of protein-carboxyl methylation and demethylation was studied in intact blood platelets. Platelets rapidly incorporated L-[methyl-3H]methionine and after a...
The cycle of protein-carboxyl methylation and demethylation was studied in intact blood platelets. Platelets rapidly incorporated L-[methyl-3H]methionine and after a delay of about 20 min, they evolved [3H]methanol. This evolution, and the amount of [3H] methanol liberated by treatment with base, was inhibited in a dose-dependent fashion by the cyclic nucleotide phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine, papaverine, dipyridamole, and RA233 (2,6-bis(diethanolamino)-4-piperidinopyrimido[5,4-d] pyrimidine). Each of these compounds increased the incorporation of [3H]methionine into platelets. The effects of RA233 were studied in more detail. Inhibition of [3H]methanol production was not potentiated by stimulators of the adenylate cyclase or the guanylate cyclase. The majority of the base-labile radioactivity was trichloroacetic acid precipitable. Thin layer chromatography of extracts of platelets incubated with L-[35S]methionine showed that RA233 did not induce a cellular accumulation of [35S]S-adenosylhomocysteine, and that it actually increased the amount of cellular [35S]S-adenosylmethionine. Discontinuous polyacrylamide gel electrophoresis at acid pH using the cationic detergent benzyldimethyl-n-hexadecylammonium chloride of platelets incubated with [3H]methionine showed incorporation of radioactivity into more than 30 protein bands, including one which co-migrates with calmodulin. The incorporation into the majority of these bands was inhibited by RA233 in a dose-dependent fashion. It is suggested that caution should be used in ascribing the pharmacological effects of known phosphodiesterase inhibitors to increases in cyclic nucleotides, because some of these effects could be due to inhibition of protein carboxyl methylation.
Topics: 1-Methyl-3-isobutylxanthine; 3',5'-Cyclic-AMP Phosphodiesterases; Blood Platelets; Dipyridamole; Humans; Hydrogen-Ion Concentration; Hydrolysis; Methionine; Mopidamol; Papaverine; Protein Methyltransferases; Protein O-Methyltransferase; S-Adenosylmethionine
PubMed: 6198323
DOI: No ID Found -
European Journal of Cancer & Clinical... Jun 1989The pyrimido-pyrimidine derivatives RA233 and RX-RA85, which are potent inhibitors of platelet and tumour phosphodiesterases, were developed as antitumour agents....
The pyrimido-pyrimidine derivatives RA233 and RX-RA85, which are potent inhibitors of platelet and tumour phosphodiesterases, were developed as antitumour agents. Clinical as well as animal studies suggest a tumour type specific, although moderate, antitumour activity for RA233. In our search for more potent congeners of RA233, we found that RX-RA85 was cytotoxic for cultured B16 melanoma and Lewis lung carcinoma cells at drug concentrations above 4 micrograms/ml whereas RA233 concentrations up to 400 micrograms/ml were tolerated. When tested for their effects on cell cycle distribution, RX-RA85 was 100-fold more potent than RA233 in producing an increase in the proportion of cells in S and G2 + M phase in 3LL cells. Progression of 3LL cells through the cell cycle was delayed for 5 h by RA233 treatment, whereas RX-RA85 was ineffective. In contrast, B16 cells responded poorly to either drug. The effects of both compounds were not only tumour cell specific but also dependent on the stage of tumour cell growth (drugs added to synchronously vs. asynchronously growing cultures). In the case of RX-RA85, the potency to affect tumour cell cycle distribution was highly dependent on tumour cell number, making the potential of this drug as an antitumour agent somewhat limited.
Topics: Animals; Cell Cycle; Cell Line; Flow Cytometry; Lung Neoplasms; Melanoma, Experimental; Mice; Mopidamol; Phosphodiesterase Inhibitors; Pyrimidines; Tumor Cells, Cultured
PubMed: 2753057
DOI: 10.1016/0277-5379(89)90152-1