New medical therapies for glaucoma

Primary open angle glaucoma remains the leading cause of blindness world wide. The most recently available pharmaceutical agents for control of intraocular pressure are the alpha-2 agonist, a topical carbonic anhydrase inhibitor and a prostaglandin. A brief overview, contrasting these three different classes of agents, including potential side effects is presented.     

Vaginal treatment with a prostaglandin F2 alpha derivative (alfaprostol) for inducing labor in pregnancy at term

The effectiveness and acceptability of Alfaprostol (an analog of PGF2 alpha) in inducing labor were assessed in 20 pregnant women at term. All subjects had no spontaneous uterine activity before treatment and the mean (M +/- SE) Bishop score was 2.45 +/- 0.21. The drug was administered by vaginal route at the dose of 10 mg every 3 hours. Regular uterine contractions appeared in all patients and delivery occurred in 85% of the patients after a mean time of 9h50min +/- 0h55min following the start of treatment. The mean dose of Alfaprostol utilized to achieve delivery was 29.4 +/- 2.0 mg. No major side effects were noted in the mothers and their fetuses at any time during treatment. Two patients exhibited vomiting. The Apgar score of all newborns at birth was 8 or more. These results suggest the usefulness of Alfaprostol to induce labor in pregnant women at term, as it has oxytocic activity without adverse effects on either the mother or the fetus.     

A multivalent approach towards linked dual-pharmacology prostaglandin F receptor agonist/carbonic anhydrase-II inhibitors for the treatment of glaucoma

Lowering of intra-ocular pressure is the primary pharmacologic approach for the treatment of glaucoma and a number of distinct mechanisms of action have been clinically validated. Targeting of multiple mechanisms in combination therapies has proven effective both clinically and commercially although potential improvements with regards to efficacy, tolerability and dosing frequency remain. Application of Theravance’s multivalent approach to drug discovery towards linked dual-pharmacology prostaglandin F receptor (FP) agonist/carbonic anhydrase (CA)-II inhibitor compounds is described. Compound 29 exhibits weak potency (pEC₅₀ = 5.7, IA >1.0) as an FP agonist with high binding affinity (pK_i = 8.1) to the CA-II enzyme, and has comparable corneal permeability to the CA-II inhibitor dorzolamide.     

Bovine bile derivative treatment for cancer-a critical evaluation

Bovine bile derivative, a material reported to be effective in cancer chemotherapy, was administered to 31 patients with malignant disease. In 22 cases the results were considered evaluable. In one of the 22 there was a suggestion of antitumor response. In almost all patients diarrhea and phlebitis developed and in 11 these complications necessitated cessation of therapy.     

Calcium ionophore activity of a prostaglandin B1 derivative (PGBx).

A water soluble derivative of PGB₁, designated PGB_X, has been found to stimulate the release of Ca²⁺ from fragmented sarcoplasmic reticulum and heart mitochondria; its activity is almost two orders of magnitude greater than other prostaglandins. PGB_X demonstrates ionophoretic activity in its ability to transfer Ca²⁺ from an aqueous to an organic phase.     

EPR study of ferric native prostaglandin H synthase and its ferrous NO derivative

Purified prostaglandin H synthase (EC 1.14.99.1) apoprotein, a polypeptide of 72 kDA, was titrated with hemin and EPR spectra of high-spin ferric heme were observed at liquid-helium temperature. With up to one hemin per polypeptide, a signal at g = 6.6 and 5.4, rhombicity 7.5%, evolved owing to specifically bound, catalytic active heme. At higher heme/polypeptide ratios signals at g = 6.3 and 5.9 were observed which were assigned to non-specific heme with no catalytic function. In microsomes from ram seminal vesicles the native enzyme showed the signal at g = 6.7 and 5.2 which could not be increased by the addition of hemin. Cyanide, an inhibitor of the enzyme, reacted at lower concentrations with the specific heme abolishing its signal at g = 6.6 and 5.4. Higher concentrations of cyanide were needed for the disappearance of the signal of non-specific heme. The reduced enzyme reacted with NO and formed two types of NO complexes. A transient complex, with a rhombic signal at gx = 2.07, gz = 2.01 and gy = 1.97, was assigned to a six-coordinate complex. The final, stable complex showed an axial signal at g = 2.12 and g = 2.001 and was assigned to a five-coordinate complex, where the protein ligand was no longer bound to the heme iron. Neither type of signal showed a hyperfine splitting from nitrogen of histidine indicating the absence of a histidine-iron bond in the enzyme. From these results and the similarity of the EPR signal at g = 6.6 and 5.4 to the signal of native catalase (EC 1.11.1.6) we speculated that tyrosinate might be the endogenous ligand of the heme in prostaglandin H synthase.     

Double isotope derivative dilution method for the determination of prostaglandin F and E type metabolites in urine

This method was developed for the quantitative determination of the main urinary metabolite (MUM) of prostaglandin (PG) F and E type in man or experimental animal. This method was based on the extraction of PG-MUM after addition of ³H-PG-MUM, the esterification with ¹⁴C-acetic anhydride and the separation and purification by column chromatography. Excretion values of adult men were PGF-MUM 1.46–15.01 μg/8 hr (n=11), PGE-MUM 0.82–15.42 μg/8 hr; and with women, PGF-MUM 0.41–7.75 μg/8 hr (n=11), PGE-MUM 0.60–11.39 μg/8 hr.     

A simple isotope derivative assay for prostaglandins and prostaglandin metabolites. I. Assay of e-type prostaglandins.

Prostaglandins of the E series may be reduced with [³H]borohydride to their corresponding counterparts of the F series: during reduction a tritium label is incorporated into the molecule. We describe a simple assay based on this reaction which can be used to measure E-type prostaglandins, and with slight modifications, to measure F-, A-, and D-type prostaglandins, as well as the 15-keto and 13,14-dihydro-15-keto metabolites. The assay will estimate 1–10 ng PGE compounds (～10^?11–10^?12 moles) but some prior purification of the sample is necessary.     

Double isotope derivative dilution method for the determination of prostaglandin F and E type metabolites in urine.

This method was developed for the quantitative determination of the main ureinary metabolite (MUM) of prostaglandin (PG) F and E type in man or experimental animal. This method was based on the extraction of PG-MUM after addition of 3H-PG-MUM, the esterification with 14C-acetic anhydride and the separation and purification by column chromatography. Excretion values of adult men were PGF-MUM 1.46--15.01 microgram/8 hr (n=11), PGE-MUM 0.8*--15.42 microgram/8 hr; and with women, PGF-MUM 0.41--7.75 microgram/8 hr (n=11), PGE-MUM 0.60--11.39 microgram/8 hr.     

Studies of the cation binding properties of an oligomeric derivative of prostaglandin B1

The ionophoretic activity of PGBx, an oligomeric mixture synthesized from 15-dehydro PGB1, with different cations was measured using arsenazo III-entrapped liposomes. The order of ionophoretic activity was Zn2+ greater than Co2+ greater than Mn2+ greater than Cu2+ greater than Ca2+ greater than Ba2+ greater than Sr2+ greater than Mg2+. The intrinsic fluorescence of PGBx was quenched by the binding of divalent cations as well as by La3+ and H+. Quenching by K+ and Na+ was minimal. The order of quenching strength of divalent cations was Zn2+ greater than Co2+ greater than Cu2+ = Mn2+ greater than Ca2+ greater than Ba2+ greater than Sr2+ greater than Mg2+. Binding affinities of these cations determined by a murexide indicator method were in good agreement with that determined by the fluorescence quenching reaction. The cation binding affinity of PGBx in aqueous solutions correlates with the ionophoretic activity in liposomes. The binding affinity for K+ was estimated from the inhibition by K+ of Ca2+ binding by PGBx. Although PGBx has a lower selectivity for divalent cation binding than the ionophore A23187, the characteristics of the binding affinity of these two compounds for various ions were similar. The pK of PGBx as determined by fluorescence quenching was 6.7. The molecular weight of the divalent cation binding unit was estimated to be about 680, with each PGBx molecule having three such binding sites. The binding of Ca2+ to such a site is one-to-one.     

Abortion induced by RU 486: importance of its combination with a prostaglandin derivative

The antiprogesterone steroid RU 486 (17 beta-hydroxy-11 beta-(4-dimethylaminophenyl l)-17 alpha-(prop-1-ynyl) estra-4,9-dien-3-one), orally administered once (600 mg), is an efficient contragestive agent in approximately 80% of pregnant women who have been amenorrheic for up to 41 days. Later on, its use is not recommended since after 41 day of amenorrhea there is an increase in the number of incomplete expulsions. A vaginal suppository of 1 mg Gemeprost, a synthetic PG-E1 analogue, has been prescribed 36-48 hrs. after the administration of RU 486. Such a suppository cannot provoke the interruption of the pregnancy by itself. In 106 women seeking for the interruption of pregnancy, and who were amenorrheic for 49 days or less, RU 486 plus prostaglandin association led to the interruption of pregnancy in all cases, and no further instrumental intervention was required. This preliminary report suggests that this method is an efficient alternative to conventional techniques available presently.