Dose dependent inhibition of B-16 melanoma growth in vivo by a synthetic analogue of PGE2

Daily intratumor administration of 16,16-dimethyl-PGE2-methyl ester in two different dosages inhibited tumor growth in C57Bl/6J mice bearing subcutaneous B-16 melanomas. The larger dose (20 microgram/day/mouse) produced a 68% decrease in tumor volume, a 69% decrease in tumor weight and a 60% decrease in the number of cells in mitotic phase. The smaller dose (10microgram/day/mouse) was one fifth less effective than the 20microgram dose but produced similar changes. Histological examination of tumors revealed no significant differences either in the inflammatory cell population or the amount of necrosis in the control and di-M-PGE2-treated tumors.     

Intramuscular 16-phenoxy PGE2 ester for pregnancy termination

A new PGE₂ derivative (16-phenoxy PGE₂ methyl sulfonylamide = sulprostone) was administered by the i.m. route to 48 women pregnancy in any of the three trimesters. The indications for pregnancy interruption were either serious medical problems in intact pregnancies (21 cases) or due to fetal death in utero (27 cases). Single doses of 500 μg were repeated every 4 hours in the former group or every 6 hours in the latter category for a maximum period of 24 hours. The treatment was successful in 81% of intact pregnancies and in 92.6% of fetal death cases with an overall mean induction interval of 12.9 hours. More than half the subjects did not experience any side effects apart from mild or moderate uterine colics. An overall mean of 1.4 episodes of vomiting or diarrhoea per induction trial was quite acceptable from the clinical point of view. The absence of serious complications in the group of critically sick women speaks in favour of the relative safety of the drug.     

Utility of d4-PGE2 as an internal standard to quantify endogenous levels of PGE1, PGE2, 190H PGE1 and 190H PGE2 in human seminal fluid by GC-MS-SIM

Four prostaglandins-PGE₁, PGE₂, 190H PGE₁ and 190H PGE₂-were quantified in human seminal fluid by GC-MS-SIM using only the internal standard, d₄-PGE₂. Methods and calculations were developed to minize errors inherent in using only one internal standard for quantifying four closely related prostaglandins. Preliminary data concerning the statistical significance of the differences found between PGE and 190H PGE levels in fertile, azospermic and oligospermic men are reported.     

Effects of PGE1 or PGE2 on luteal function in pseudopregnant rats

Effects of PGE₁ or PGE₂ on luteal function were studied in 163 pseudopregnant rats. PGE₁ (10, 100, or 300μg) given intrauterine every 6 hr did not shorten pseudopregnancy (P < 0.05), however, the same doses of PGE₂ given intrauterine every 6 hr advanced luteolysis (P < 0.05). PGE₁ (100 or 300μg) given every 4 hr intramuscular maintained levels of progesterone in peripheral blood above controls (P < 0.05) while 100 or 300μg of PGE₂ hastened the decline in progesterone (P < 0.05). The antiluteolytic effect of PGE₁ was not via an inhibition of PGF secretion (P < 0.05) by the uterus or by induction of ovulation in treated animals. Moreover, PGE₁ (100, 200, or 500μg) given intramuscular every 4 hr from day 4 of pseudopregnancy until the next proestrus delayed luteal regression around 3 days (P < 0.05). PGE₂ at doses of 100, 200, or 500μg every 4 hr given intramuscular consistently shortened pseudopregnancy (P < 0.05). Lower doses were without effect (P < 0.05). Based on the above data it is concluded that PGE₂ is consistently luteolytic whereas PGE₁ is not luteolytic in pseudopregnant rats and that PGE₁ may be an antiluteolysin.     

Inhibition by 16, 16-dimethyl PGE2 of ethanol-induced gastric mucosal damage and leukotriene B4 and C4 formation

The effects of PGE₂ and its stable analogue, 16, 16 dimethyl PGE₂ (dmPGE₂) were investigated on ethanol-induced gastric mucosal haemorrhagic lesions and leukotriene formation in the rat. Exposure of the rat gastric mucosa to ethanol , produced a concentration-related increase in the mucosal formation of leukotriene B₄ (LTB₄) which was correlated with macroscopically-apparent haemorrhagic damage to the mucosa. Challenge with absolute ethanol likewise enhanced the mucosal formation of LTC₄ whereas the mucosal formation of 6-keto-PGF_1α was unaffected. Challenge of the rat gastric mucosa with ethanol induced a concentration-dependent increase in the formation of LTB₄ and LTC₄, but not 6-keto PGF_1α. Pretreatment with PGE₂ (200–500μg/kg p.o.) prevented the haemorrhagic mucosal damage induced by oral administration of absolute ethanol but not the increased formation of leukotrienes by the mucosa. In contrast, pretreatment with a high dose of dmPGE₂ (20μg/kg p.o.) prevented both the gastric mucosal lesions and the increase mucosal leukotriene formation. The differences in the effects of these prostaglandins may be related to the nature or degree of protection of the gastric mucosa. Thus, high doses of dmPGE₂ but not PGE₂ may protect the cells close the luminal surface of the mucosa and hence reduce the stimulation of leukotriene synthesis by these cells.     

Plasma levels of 13,14-dihydro-15-keto PGE2 after vaginal application of a new PGE2 film

To determine the release and absorption profile of prostaglandin E₂ from a new vaginal film formulation containing 850 μg PGE₂, serial plasma levels of 13,14-dihydro-15-keto PGE₂ were measured by radioimmunoassay in pregnant women between 16 and 18 weeks gestation. A control group, using placebo vaginal film was included in the study. There was a somewhat uniform increase in the plasma levels of the PGE₂ metabolite, reaching peak levels between 4 and 6 hours after application of the film. The findings suggest that this drug formulation could be used clinically when slow constant release of the prostaglandin is required over a period of hours such as in pre-induction cervical ripening of term pregnancy.     

Metabolism of viprostol — A synthetic vasolidator PGE2 analog

Metabolic studies were done with ¹⁴C-Viprostol (I) administered by various routes (I.V., oral and topical) to six animal species and to man. Total radioactivity and metabolic profiles were analyzed in plasma, tissues and excreta. The main metabolites were isolated and identified by capillary GC/MS.Plasma and urinary metabolic profiles were qualitatively similar across species, with two major metabolic reactions being predominant: rapid hydrolysis to the pharmacologically active free acid (II)_ and oxidation of the alpha-chain to dinor and tetranor acids (III, IV). In the monkey and man, reduction of the 9-keto group lead to PGF₂ type metabolites (VI–VIII). In the rat, omega oxidation of the beta-chain occurred as well, resulting in the formation of dicarboxylic acids (V).     

Receptor binding in various tissues of PGE2, PGF2α and sulprostone, a novel PGE2-derivative

Sulprostone is a tissue-specific PGE₂-derivative with high abortifacient activity in various species including man. The dissociation constant K_D of the receptor binding of this compound was compared with PGE₂ and PGF_2α in various tissue preparations of different species. A structure-binding relationship was developed from competition curves after a logit/log transformation. It is demonstrated that the relative affinities of Sulprostone, PGE₂ and PGF_2α remain essentially constant in all the tissues investigated. It is concluded that the tissue-specificity of Sulprostone cannot be ascribed to structural differences of the receptor molecule.     

A dose-response comparison of PGA2, PGE1 and PGE2 using the phenylephrine-stimulated perfused oviduct of the rabbit

The phenylephrine-stimulated perfused oviduct of the rabbit was evaluated as a model for studying the activity of prostaglandins that produce inhibition of the oviducal smooth muscle. Elevation of the normal “tone” of the oviduct by perfusing phenylephrine through the lumen permitted quantitation of the responses to PGA₂, PGE₁ and PGE₂ by measuring the magnitude of the inhibitory response produced by the agents. PGE₂ was relatively more potent, efficacious and specific for the oviduct than PGA₂ or PGE₁. It was concluded that the model was suitable for comparative dose-response studies of PGA₂, PGE₁ and PGE₂ and their analogs.     

Basal level of human platelet prostaglandins: PGE1 is more elevated than PGE2

Radioimmunoassays of platelet prostaglandins E₁ and F_1α in platelet rich plasma or platelet suspension, demonstrate that both PGE₁ and PGF_1α are present at higher concentrations than prostaglandins E₂ and F_2α. Gas chromatography — mass spectrometry determinations of prostaglandins E₁ and E₂ in resting washed platelets confirm this difference. Lastly, there is a greater incorporation of [1-¹⁴C] acetate into prostaglandins E₁ and F_1α compared to that into prostaglandins E₂ and F_2α.     

Prostaglandin E1 or E2 (PGE1, PGE2) prevents premature luteolysis induced by progesterone given early in the estrous cycle in ewes

The objective of this study was to determine whether prostaglandin E₁ (PGE₁) or prostaglandin E₂ (PGE₂) prevents premature luteolysis in ewes when progesterone is given during the first 6 days of the estrous cycle. Progesterone (3 mg in oil, im) given twice daily from Days 1 to 6 (estrus = Day 0) in ewes decreased (P < 0.05) luteal weights on Day 10 postestrus. Plasma progesterone concentrations differed (P < 0.05) among the treatment groups; toward the end of the experimental period, concentrations in jugular venous blood decreased (P < 0.05) compared with the other treatment groups. Plasma progesterone concentrations in ewes receiving PGE₁ or PGE₁ + progesterone were greater (P < 0.05) than in vehicle controls or in ewes receiving PGE₂ or PGE₂ or PGE₂ + progesterone. Chronic intrauterine treatment with PGE₁ or PGE₂ prevented (P < 0.05) decreases in plasma progesterone concentrations, luteal weights, and the proportion of luteal unoccupied and occupied LH receptors on Day 10 postestrus in ewes given exogenous progesterone, but did not affect (P > 0.05) concentrations of PGF_2α in inferior vena cava blood. Progesterone given on Days 1 to 6 in ewes advanced (P < 0.05) increases in PGF_2α in inferior vena cava blood. We concluded that PGE₁ or PGE₂ prevented progesterone-induced premature luteolysis by suppressing loss of luteal LH receptors (both unoccupied and occupied).     

Nasal vasoconstrictor activity of a novel PGE2 analog

A novel PGE₂ analog (CL 116,069) was shown to be effective in dogs as a nasal decongestant. Threshold doses were approximately 0.1 μg/kg with intravenous administration and between 0.08 and 4 μg with topical administration. CL 116,069 was compared to 17-phenyl-trinor PGE₂ (CL 116,147), a compound recently studied in humans, and xylometazoline, a well-known nasal decongestant. When given i.v., efficacious doses of xylometazoline tended to raise blood pressure and be shorter acting than the PGs, which did not affect blood pressure. When given topically, all three were long-acting. CL 116,069 usually had the lowest threshold and CL 116,147 usually induced the smallest response. All three agents were more effective than PGE₁ or PGE₂. A 30-day (b.i.d., topical) toxicity test with CL 116,069 produced no inflammation or nasal pathology and no loss in tissue sensitivity. $\text{In}$$\text{vitro}$ examination of xylometazoline and CL 116,069 for vascoconstrictor activity on dog isolated mucosa revealed a response profile similar to that observed with these agents $\text{in}$$\text{vivo}$; i.e., the magnitude of response was comparable for both agents but the t $\text{1}\text{2}$ was only 74 minutes for xylometazoline and greater that 6.5 hours for CL 116,069. The data suggest that CL 116,069 may provide a therapeutic alternative in which constriction of the nasal blood vessels need not be associated with a generalized vasoconstrictor liability.     

Sex differences in gastric mucosal protection after 16, 16-dimethyl PGE2 and lithium chloride

While the incidence of duodenal ulcer disease has been documented to be greater in men than in women, this observation has not been previously noted in animal studies of the upper gastrointestinal tract. In this study, we questioned whether the cytoprotective properties of 16, 16-dimethyl PGE₂ were sex-related by comparing the degree of ethanol-induced hemorrhagic gastritis in male and female rats pretreated with 16,16-dimethyl PGE₂ or lithium chloride. Animals receiving 16,16-dimethyl PGE₂ or lithium chloride had significantly less ethanol-induced hemorrhagic gastritis (1.17±0.15 and 1.24±0.13, respectively, p<0.001) when compared with controls (2.69±0.10). Female rats treated with 16,16-dimethyl PGE₂ had 59% less hemorrhagic gastritis than male rats treated similarly (0.76±0.14 vs 1.86±0.19 respectively, p<0.001). This sex-related difference in hemorrhagic gastritis was not noted in male and female rats receiving lithium chloride (1.24±0.15 vs 1.23±0.27, respectively). However, female rats treated with 16, 16-dimethyl PGE₂ had significantly less hemorrhagic gastritis when compared with female rats receiving lithium chloride (0.76±0.14 vs 1.24±0.15 respectively, p<0.05).These findings suggest that the protective properties of 16, 16-dimethyl PGE₂ are sex-related while those of lithium chloride are not.     

Dose response relation of the renal effects of PGA1, PGE2, and PGF2α in dogs

The effects of the three prostaglandins A₁, E₂, and F_2α on renal blood flow, glomerular filtration rate (GFR), fluid excretion, and urinary output of Na, K, Ca, Cl, and solutes were evaluated at a dose range of 0.01 – 10 μg/min. The prostaglandins were infused into the renal artery of dogs. GFR was not significantly altered by the PGs. PGA₁ increased renal blood flow by approximately of the control at 0.01 μg/min without dose dependence at higher infusion rates. It had only little effects which were not dose dependent on fluid and electrolyte output. The effects of PGE₂ on renal blood flow, fluid, sodium, and chloride excretion were dose dependent with a steep slope of the dose response curve between 0.1 and 1.0 μg/min. Blood flow was increased maximally by 80 %, urine volume by more than 400 %. PGF_2α had no effect on renal blood flow, whereas urinary output was increased to approximately the same maximal level as by E₂ although ten times higher doses were needed. Potassium excretion was less influenced than the excretion of Na and Cl and osmolar clearance was less increased than urine volume by all three prostaglandins.It is concluded that if a PG is involved in the regulation of the renal fluid or electrolyte excretion it is likely to be of the PGE-type. A PGA could only be involved in regulation of renal hemodynamics, whereas PGF although effective in the kidney exerts its effects at doses too high to have physiological significance.     

Inotropic effect of PGE1 and PGE2 on isolated rat atria. Influence of adrenergic mechanisms

The effects of a wide range of PGE₁ and PGE₂ concentrations on the isometric developed tension of isolated rat atria beating spontaneously or paced at a fixed rate, were explored. PGE₁ only produced a negative inotropic effect (NIE), whereas PGE₂ elicited a biphasic inotropic action; negative at low concentrations and positive (PIE) at higher ones. Phenoxybenzamine and phentolamine failed to modify either the NIE or the PIE, but subthreshold exogenous norepinephrine abolished the NIE, suggesting a presynaptic inhibitory effect of PGEs on the adrenergic neurotransmitter release. Auricles pretreated with subthreshold norepinephrine react with a PIE to PGE₁, but not to PGE₂. On the contrary in the presence of subthreshold methoxamine the PIE of PGE₂ was increased whereas the action of PGE₁ was not modified.     

The effects of prostaglandins PGE1, PGE2, PGF1a, and PGF2a on canine synovial perfusion

In these experiments we have examined the effects of PGE₁, PGE₂, PGF_1α and PGF_2α on synovial perfusion in the normal canine synovial microcirculation. The effects of the drugs on synovial perfusion were determined indirectly from the changes produced in the rate of clearance of ¹³³Xenon from the joint by their intra-articular injection. Prostaglandins PGE₁ and PGE₂ were found to be strongly vasodilator with PGE₁ being the more active. PGF_1α appeared to have little or no vasoactive properties in doses up to 1 ugm. (2.8 × 10^−5M) in our I preparation while PGF_2α was vasodilator at this high dosage only. Neither SC19920 nor diphloretin phosphate antagonised the effects of PGE₁ in these experiments.     

Circulating and urinary metabolites of PGE2 and PGF2a

Fig. 1 summarizes the structures of primary PGE₂ and PGF_2a (upper line), their initially formed 15-ketodihydro-metabolites which appera early in blood after release (middle), and their β- and ω-oxidized metabolites, which appear later and remain longer in the circulation and also dominate the urinary profile (lower line). No single compound can be put forward as the ideal assay parameter: depending on aim and design of the study, either of these compounds may be monitored. The chemical instability of PGE compounds should however be kept in mind: generally it is safer to induce degradation by alkali treatment into a stable product prior to assay.