L
`E
`C
`T
`U
`R
`E
`From PGF2a-Isopropyl Ester to Latanoprost:
`A Review of the Development of Xalatan
`The Proctor Lecture
`
`Johan Wilhelm Stjernschantz
`
`T he research that led to the concept of using prostaglandins
`
`for reduction of intraocular pressure (IOP) has been dis-
`cussed by Bito and goes back to the early 1980s, when it was
`shown that PGF2a effectively reduces IOP in monkeys.1 Be-
`cause the IOP-reducing effect in primates was found to be
`profound and of long duration, it was of obvious interest to
`investigate whether prostaglandins could be developed into
`drugs for glaucoma treatment. A fruitful collaboration between
`Columbia University (New York, NY) and Pharmacia (Uppsala,
`Sweden), a pharmaceutical company, was initiated. As a result
`of the collaboration, a new glaucoma drug Xalatan was devel-
`oped. The purpose of this article is to present a review of the
`research that lead to the identification of latanoprost, and the
`development of Xalatan. Some relevant recent and previously
`unpublished data have been included as well. The experimen-
`tal protocols of all animal studies performed complied with the
`tenets of the ARVO Statement on the Use of Animals in Oph-
`thalmic and Vision Research, and all protocols were submitted
`for review and approval to the local Ethics Committee for
`Animal Experimentation. Protocols for clinical studies were
`submitted to the appropriate Ethics Committee/Internal Re-
`view Board and the Declaration of Helsinki (1964) with subse-
`quent revisions was adopted. Details concerning the experi-
`mental procedures of the previously unpublished results are
`given in the figure and table texts.
`
`PGF2a-Isopropyl Ester as a Prototype
`Prostaglandin Drug for Glaucoma Treatment
`The first approach to render prostaglandins suitable for glau-
`coma treatment was esterification of the carboxylic acid to
`improve the bioavailability2 and reduce the side effects. Several
`esters of PGF2a were synthesized and tested for IOP-reducing
`effect and side effects.3 One of the best of these prodrugs of
`PGF2a was the isopropyl ester (IE), but many other carboxylic
`acid esters, and di-, tri-, and tetra-esters and lactones of PGF2a
`were prepared and tested in addition (Bito LZ, Resul B, unpub-
`lished results, 1985). Similar experiments were also performed
`by researchers at Allergan Pharmaceuticals (Irvine, CA).4 Other
`companies (e.g., Ueno Fine Chemicals Industry, Osaka, Japan,
`and Alcon Laboratories, Fort Worth, TX) subsequently adopted
`the isopropyl ester prodrug concept for their respective pros-
`
`From the Department of Neuroscience, Unit of Pharmacology,
`Uppsala University, Uppsala, Sweden.
`Submitted for publication July 17, 2000; accepted September 8,
`2000.
`Commercial relationships policy: F, I, P. (The author is a former
`employee of Pharmacia and is a recipient of a research grant from
`Pharmacia, but has no commercial interest in Xalatan.)
`Corresponding author: Johan Stjernschantz, Department of Neu-
`roscience, Unit of Pharmacology, Box 593, Uppsala University Biomed-
`ical Center, S-751 24 Uppsala, Sweden.
`johan.stjernschantz@neuro.uu.se
`
`1134
`
`taglandin analogues (isopropyl unoprostone and travoprost,
`respectively).
`PGF2a-IE is a very efficacious and potent IOP-reducing agent
`in cats, dogs, and monkeys.2,5–7 Comparable reductions of IOP
`with PGF2a tromethamine salt requires a 10 to 100 times
`higher dose in monkeys.2,8 –10 Thus, esterification of PGF2a
`with isopropanol
`increased the bioavailability substantially.
`Overall, PGF2a-IE was found to be a very good IOP-reducing
`agent in many species except rabbits, in which a pressure
`increase frequently is induced by a breakdown of the blood–
`aqueous barrier. It is interesting that whereas cats exhibited
`distinct signs of ocular pain and discomfort (e.g., closure of the
`lids and lacrimation) unanesthetized monkeys usually did not
`(Stjernschantz J, unpublished results, 1988). In addition, in cats
`and dogs PGF2a and its esters are potent miotics.11
`In the first clinical trial with PGF2a-IE, which had the char-
`acter of a pilot test, no or a minimal IOP-reducing effect was
`observed in patients with glaucoma, probably because difficult
`cases were selected, refractory to all medical treatment (un-
`published results, Pharmacia). Despite these discouraging re-
`sults Villumsen and Alm,12 in cooperation with Pharmacia,
`started a systematic investigation to determine the IOP-reduc-
`ing effect and side effects of PGF2a-IE and found that the drug
`indeed effectively reduced IOP in a dose-dependent manner in
`healthy volunteers. However, the IOP-reducing effect was ac-
`companied by conjunctival hyperemia and ocular irritation
`similar
`to the side effects
`seen in studies with the
`tromethamine salt of PGF2a.13,14 The highest dose (10 mg) of
`PGF2a-IE caused pain and photophobia in all individuals.12 A
`dose of 0.5 mg twice daily was chosen for further studies in
`patients, and this dose, as well as a dose of 1 mg twice daily,
`was found to reduce IOP significantly, alone and in combina-
`tion with timolol.15–18
`However, many patients reported side effects such as for-
`eign-body sensation and conjunctival hyperemia, and it be-
`came questionable whether PGF2a-IE would offer any advan-
`tage over the already-established glaucoma medications. A
`particular problem was the irritative response to the drug. In
`animal experiments, it has been shown that PGF2a-IE induces
`albumin leakage in the iris and the ciliary body of monkeys at
`a dose of 1 mg,19 and it is possible that the 10 times higher dose
`previously used in healthy individuals12 induces edema in the
`anterior uvea that causes pain and photophobia.
`
`Effect of PGF2a-IE on the Uveoscleral Outflow
`Mode of Action
`The first evidence that PGF2a and its isopropyl ester reduces
`IOP through a mechanism based on increased uveoscleral
`outflow came from the studies by Crawford and Kaufman20
`and Nilsson et al.6 Both research groups independently of each
`other found evidence for increased uveoscleral outflow of
`aqueous humor in monkeys treated with PGF2a tromethamine
`salt or PGF2a-IE and no or minimal effect on the conventional
`
`Investigative Ophthalmology & Visual Science, May 2001, Vol. 42, No. 6
`Copyright © Association for Research in Vision and Ophthalmology
`
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`IOVS, May 2001, Vol. 42, No. 6
`
`The Proctor Lecture
`
`1135
`
`TABLE 1. Effects of PGF2a-IE, PGF2b-IE, and 11-epi-PGF2a-IE on IOP, Pupil Diameter, and Nociception in Cats and on IOP in Monkeys
`
`Cat
`
`Monkey
`
`Prostaglandin
`Analogue
`
`Dose
`(mg)
`
`Reduction in IOP
`(mm Hg)
`
`Reduction in Pupil
`Diameter (mm)
`
`PGF2a-IE
`PGF2b-IE
`11-epi-PGF2a-IE
`
`1.0
`1.0
`1.0
`
`27.5 6 1.3‡
`28.3 6 1.5‡
`0.2 6 0.5
`
`29.3 6 0.4†
`0.0 6 0.0
`27.0 6 0.7†
`
`Irritation*
`
`2.7 6 0.2†
`1.5§
`1.0§
`
`Dose
`(mg)
`
`Reduction in IOP
`(mm Hg)
`
`FP Receptor EC50 Value
`(moles/l)
`
`3.0
`1.5
`2.4
`
`22.5 6 0.3†
`21.1 6 0.8
`22.0 6 0.9
`
`1.0 3 1028
`5.6 3 1026
`3.3 3 1028
`
`The values are based on the maximum difference between the experimental and contralateral control eyes (mean 6 SEM; n 5 5–6). The FP
`receptor EC50 values are based on results of in vitro tests performed on cat irides with the corresponding prostaglandin acids. Partly reproduced,
`with permission, from Resul et al., Surv Ophthalmol. 1997;41(suppl):S47–S52.
`* Arbitrary scale of 0 to 3 (see Fig. 3).
`† P , 0.001.
`‡ P , 0.005.
`§ Estimated mean value.
`
`outflow.6,20,21 Indirect evidence for a similar mechanism in
`humans was also obtained in two separate studies: PGF2a-IE
`was not found to have any effect on aqueous humor produc-
`tion or outflow facility.12,22 Thus, the most reasonable expla-
`nation for the IOP reduction was increased uveoscleral out-
`flow, although it could not be excluded that the drug may have
`reduced the episcleral venous pressure, too. It is important to
`note that in neither of the two clinical studies was any evi-
`dence found of a significant effect of PGF2a-IE on the blood–
`aqueous barrier.12,22
`
`Rationale of Receptor Selectivity for Elimination
`of Side Effects
`The preclinical and clinical studies with PGF2a-IE demon-
`strated that prostaglandins of the F type could be useful in the
`treatment of glaucoma, but it was not realistic to develop
`PGF2a-IE into a glaucoma drug for broader use, because of the
`side effects. Patients with severe disease could have endured
`treatment with the drug for some time. The question thus arose
`of whether it would be possible to separate the IOP-reducing
`effect from the side effects—primarily the irritative and hyper-
`emic effects— by changing the receptor profile of PGF2a
`through chemical modification. It should be recalled in this
`context that the classification of the prostanoid receptors in
`the mid 1980s was somewhat ambiguous, based on conven-
`tional pharmacologic experiments only.23–25 However, early
`experiments that we had performed with two epimers of
`PGF2a-IE, namely PGF2b-IE and 11-epi-PGF2a-IE indicated that
`the miotic and IOP responses to PGF2a-IE could be distinctly
`separated by these two epimers in cats (Table 1). PGF2b-IE
`reduced IOP with no miotic effect, whereas 11-epi-PGF2a-IE
`was a potent miotic with little effect on IOP. Furthermore, the
`epimers also differed from PGF2a-IE with respect to the noci-
`ceptive response (Table 1) and the hyperemic response,
`PGF2b-IE, being a much stronger vasodilator
`than both
`PGF2a-IE and 11-epi-PGF2a-IE (unpublished results; Pharmacia).
`Thus, it appeared possible to separate the different ocular
`responses from each other, at least partly, and there was also
`an indication that the FP prostanoid receptor, which mediates
`miosis in cats, may be involved at least partly in IOP reduction
`in monkeys.26 (Table 1).
`A critical aspect in the success of the screening work was
`the selection of appropriate animal models that would allow
`extrapolation of the results to the human eye. The cat eye
`seemed very unspecific, in that IOP reduction was brought
`about by widely different prostaglandin analogues (e.g., PGF2a,
`PGF2b, PGE2, PGA2, PGB2, and PGD2). Therefore, we regarded
`the cat eye as somewhat unpredictable with respect to the IOP
`effect in humans and used the cat eye primarily for studying
`
`the nociceptive and miotic effects, whereas conscious cyno-
`molgus monkeys were used to study the IOP-reducing effect.
`However, because young healthy monkeys usually have low
`IOP, often around 11 to 15 mm Hg, the test model was not
`ideal but was good enough to confirm whether an analogue
`had an IOP-reducing effect. The hyperemic effect was studied
`in albino rabbits, but there were no attempts to study anything
`else in the rabbit, because the rabbit eye is known to react very
`atypically to prostaglandins.27–29 Thus, the selection of ade-
`quate animal models was of paramount importance for the
`success of the project.
`
`Structure–Activity Approach and Identification of
`Phenyl-Substituted Prostaglandin Analogues
`The first approach to modifying PGF2a included various alter-
`ations of the carboxylic acid end of the molecule. The alter-
`ations comprised, for example, the alcohol and simple esters
`but generally did not result in any clear-cut improvement of the
`pharmacologic profile of PGF2a. The second approach was to
`change the stereochemistry, and the functional groups in the
`cyclopentane ring. Although this yielded some interesting an-
`alogues that offered certain advantages over PGF2a, such as
`11-epi-PGF2a,26 modifications of the cyclopentane ring re-
`sulted in no real breakthrough. The third approach was to alter
`parts of the vchain (e.g., the double bond between carbons 13
`and 14 and the 15-hydroxyl group) and to substitute part of the
`chain. However, it was well known that the 15-hydroxyl group
`is essential for biologic activity of prostaglandins, and dehydro-
`genation of the hydroxyl group results in marked loss of bio-
`logic activity.30 –31 Thus, the approach taken by the research-
`ers of Ueno Fine Chemicals Industry (Osaka, Japan) to reduce
`the side effects of PGF2a by preparing the 13,14-dihydro-15-
`keto metabolite, or modifications of this metabolite (e.g., iso-
`propyl unoprostone) renders molecules with significantly re-
`duced potency.32
`Among a group of different v-chain–modified prostaglan-
`din analogues, we quite unexpectedly noted that 17-phenyl-
`18,19,20-trinor-PGF2a-IE induced marked miosis in the cat
`without concomitant irritation, which almost all other pros-
`taglandin analogues had induced. Although there was no
`significant effect of the analogue on IOP in cats, conceptu-
`ally, the combination of marked miosis with absence of
`nociception demonstrated that it was possible to eliminate
`the nociceptive effect without losing pharmacologic activ-
`ity. In contrast to cats,33 monkeys responded to the com-
`pound with satisfactory IOP reduction.34 –35 The compound,
`which can be regarded as the breakthrough, was assigned
`the code name PhDH100A and became the lead compound
`of the group of v-chain ring-substituted prostaglandin ana-
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`1136
`
`Stjernschantz
`
`IOVS, May 2001, Vol. 42, No. 6
`
`Influence of v-Chain Length on
`Pharmacologic Profile
`This aspect was studied in detail by attaching a terminal phenyl
`ring to carbons 15-24 (Fig. 1). The analogues were studied in
`cats with emphasis on the miotic and nociceptive responses.
`Of note, attaching the aromatic ring structure to carbon 17 of
`the prostaglandin skeleton yielded an optimal compound, in
`that the FP receptor function, as evident from the miotic
`response, was not compromised, whereas the nociceptive re-
`sponse was completely abolished34 (Table 2). In bizarre con-
`trast, 16-phenyl-17,18,19,20-tetranor-PGF2a-IE with one addi-
`tional carbon atom removed from the v chain caused
`significant irritation, albeit less than PGF2a-IE. Elongation of the
`v chain beyond carbon 17 with a terminal phenyl ring at-
`tached, reduced the biologic activity34 (Table 2). However, it is
`noteworthy that most analogues with a terminal ring structure
`exhibited considerably less nociceptive effect than PGF2a-IE.
`Substitution of carbon 17 with oxygen afforded a compound
`(16-phenoxy-17,18,19,20-tetranor-PGF2a-IE) with similar phar-
`macologic profile to that of 17-phenyl-18,19,20-trinor-PGF2a-IE
`(unpublished results; Pharmacia).
`
`Influence of Different Ring Structures on the
`Pharmacologic Profile
`A large number of compounds with different ring structures
`from cyclopropyl to cycloheptyl and aromatic ring structures,
`such as phenyl, thiophen, and furyl, attached to carbon 17 (Fig.
`1) were prepared and tested. Overall, these analogues exhib-
`ited an improved side-effect profile compared with PGF2a-IE,
`albeit with somewhat different pharmacologic activity. Thus it
`appears that many different terminal ring structures attached to
`carbon 17 in the v chain reduce the side effects of PGF2a-IE.
`
`Influence of Substituents in the Ring Structure on
`the Pharmacologic Profile
`Compounds with various substitutions in the phenyl ring (Fig.
`1) were also prepared and tested for pharmacologic activ-
`ity.26,34 Introduction of a methyl group into the ortho (2) or
`meta (3) position in the phenyl ring did not appreciably
`change the miotic activity of 17-phenyl-18,19,20-trinor-PGF2a-
`IE, whereas introduction of the methyl group into the para (4)
`position dramatically reduced the activity.26,34 Obviously, the
`methyl group in the para position induces a steric hindrance in
`the receptor ligand interaction. Introduction of an electron-
`attracting trifluormethyl group into the ortho or para position
`in the phenyl ring reduced the activity of the compound,
`
`FIGURE 1.
`Series of ring-substituted analogues of PGF2a-isopropyl es-
`ter tested for effects in the eye to determine the importance of v-chain
`length, ring structures, and substituents in the phenyl ring.
`
`logues in the screening for an optimal prostaglandin ana-
`logue for glaucoma treatment.
`
`Importance of v-Chain Length, Ring Structures,
`and Substituents
`The identification of 17-phenyl-18,19,20-trinor-PGF2a-IE lead to
`medicinal chemistry experiments that were of obvious interest
`to perform to understand the critical elements in the molecules
`for attaining efficacy and selectivity in the eye. Three aspects
`seemed particularly relevant to study: (1) the influence of the
`v-chain length, (2) the influence of different ring structures,
`and (3) the influence of substituents in the ring structure on
`the pharmacologic profile of the new analogues.
`
`TABLE 2. Effect of Phenyl-Substituted PGF2a-IE Analogues with Different v-Chain Lengths on IOP, Pupil Diameter,
`Nociception, and Conjunctival Hyperemia
`
`Cat
`
`Prostaglandin Analogue
`
`16-Phenyl-17,18,19,20-tetranor-PGF2a-IE
`17-Phenyl-18,19,20-trinor-PGF2a-IE
`18-Phenyl-19,20-dinor-PGF2a-IE
`19-Phenyl-20-nor-PGF2a-IE
`
`Monkey
`Reduction in IOP
`(mm Hg)
`
`Reduction in Pupil
`Diameter
`(mm)
`
`23.9 6 0.4†
`23.9 6 0.4†
`20.6 6 0.2§
`20.6 6 0.2§
`
`21.0 6 0.0†
`29.7 6 0.3†
`24.3 6 0.6†
`22.5 6 0.6‡
`
`Irritation*
`(0–3)
`
`2.2 6 0.3†
`0.0 6 0.0
`0.7 6 0.1†
`1.3 6 0.2‡
`
`Rabbit
`Hyperemia*
`(1–5)
`
`ND
`1.8 6 0.3‡
`0.3 6 0.7
`0.6 6 0.2§
`
`The values are based on the maximum difference between the experimental and contralateral control eyes. The dose was 3 mg in monkeys,
`1 mg in cats, and 0.5 mg in rabbits (mean 6 SEM; n 5 5–6; statistical significances determined by paired t-test). ND, not determined.
`* Arbitrary scale.
`† P , 0.001.
`‡ P , 0.01.
`§ P , 0.05.
`
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`IOVS, May 2001, Vol. 42, No. 6
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`The Proctor Lecture
`
`1137
`
`whereas introduction of the group into the meta position only
`slightly reduced the activity.26,34 Substituting fluorine for the
`trifluormethyl in the ortho, meta, orpara position afforded
`compounds with marked miotic effect and no or very little
`irritant effect in the cat eye, thus indicating that the trifluor-
`methyl group may also partly change the pharmacologic activ-
`ity through a steric effect.26,34 Introduction of an electron-
`donating methoxy group into the ortho or para position
`markedly reduced miotic activity, whereas introduction of the
`group into the meta position only slightly reduced miotic
`activity.26,34 The 16-(4-methoxy)-phenyl-17,18,19,20-tetranor
`PGF2a-IE analogue had virtually no irritant effect in the cat eye
`in contrast to 16-phenyl-17,18,19,20-tetranor-PGF2a-IE (unpub-
`lished results, Pharmacia). Thus, it appears that the para posi-
`tion, and to some extent the ortho position, in the phenyl ring
`are sensitive to steric hindrance, whereas the meta position is
`much less vulnerable. However, in the ortho position electro-
`chemical forces may be important, at least in part, because an
`electron-attracting trifluormethyl group reduces the activity in
`contrast to a neutral methyl group.
`Overall, the structure–activity studies indicated that the ring
`structure on the v chain is of paramount importance for
`reducing the side effects of PGF2a-IE, and furthermore that a
`large number of modifications of the ring structure are possi-
`ble, still affording useful compounds in the eye.26,34 –36
`Saturation of the 13,14-trans double bond of 17-phenyl-
`18,19,20-trinor-PGF2a-IE was found to further improve the re-
`ceptor profile somewhat, and 13,14-dihydro prostaglandin an-
`alogues in addition exhibited improved chemical stability. The
`13,14-dihydro-15R,S-17-phenyl-18,19,20-trinor-PGF2a-IE
`ana-
`logue was selected as the new candidate drug, and the com-
`pound was given the code name PhXA34. Because the 15R
`epimer is more potent than the 15S epimer, with time the 15R
`epimer (PhXA41) became the final candidate drug. It was given
`the generic name latanoprost and is the active principle in
`Xalatan. The chemical structures of PGF2a-IE, 17-phenyl-
`18,19,20-trinor-PGF2a-IE, PhXA34, and latanoprost (PhXA41)
`are presented in Figure 2.
`
`Latanoprost
`
`As is obvious from the structure–activity studies, the reason for
`the good therapeutic index of latanoprost in the eye is its
`pharmacologic receptor profile. It can be seen in Table 3 that
`latanoprost acid is a much more selective FP prostanoid recep-
`tor agonist than PGF2a. In practical terms it is even more
`selective than 17-phenyl-18,19,20-trinor-PGF2a because it spills
`less over on the EP1 and TP receptors (Table 3). It is also
`apparent that latanoprost acid is a full agonist on the FP
`receptor, and full or near full agonist on the EP1 and EP3
`receptors, but has no, or only weak effect on prostanoid
`receptors EP2, DP, IP, and TP (Table 3). In comparison 17-
`phenyl-18,19,20-trinor-PGF2a, with the 13,14 double bond in-
`tact, is a full agonist on the FP and EP1 receptors, and a partial
`agonist on the TP receptor, but has no, or only weak effect on
`the other receptors (Table 3). Thus, increasing the flexibility of
`the v chain by saturating the 13,14 double bond has relatively
`little effect on the interaction with the FP receptor, but re-
`duces the potency on the EP1 and TP receptors, and increases
`the capacity to stimulate the EP3 receptor, albeit only at very
`high concentrations.
`Latanoprost has virtually no IOP-reducing effect in cats or
`rabbits, but induces a moderate IOP reduction in conscious
`normotensive monkeys as measured 3 to 6 hours after topical
`application. During continuous treatment with 3 mg once daily
`for 5 days the IOP reduction lasted around the clock (unpub-
`lished results; Pharmacia). In ocular hypertensive monkeys a
`good IOP-reducing effect of latanoprost has also been seen.37
`
`FIGURE 2. Chemical structures of PGF2a-IE, 17-phenyl-18,19,20-trinor-
`PGF2a-IE, 13,14-dihydro-15R, S-17-phenyl-18,19,20-trinor-PGF2a-IE (PhXA34),
`and 13,14-dihydro-15R-17-phenyl-18,19,20-trinor-PGF2a-IE (latanoprost).
`
`The absence of effects in cats and rabbits may be due to several
`factors—for example, different anatomy of the ciliary muscle
`and aqueous humor outflow pathways compared with pri-
`mates, and the absence of expression or different coupling of
`FP receptors in the ciliary muscle. Of note, recently it was
`demonstrated that the prostanoid receptor EP1 seems to medi-
`ate the IOP reduction of PGF2a in the cat.38
`
`Mode of Action
`Thorough pharmacodynamic studies in cannulated monkey
`eyes were performed to investigate the mode of action of
`latanoprost, because the mechanism could differ from that of
`PGF2a-IE due to the different receptor profiles of the com-
`pounds. Cynomolgus monkeys were treated for 5 days topi-
`cally on one eye with 3 mg latanoprost daily; the other eye
`received vehicle only and served as the control. A detailed
`description of the pharmacodynamic method has been pre-
`sented.39 The results showed that latanoprost had a statistically
`significant effect on the uveoscleral outflow, which increased
`by approximately 60% compared with the contralateral control
`eye.39,40 Neither the trabecular outflow of aqueous humor, nor
`the total outflow facility changed during latanoprost treat-
`ment.39,40
`The reason for the increase in flux of aqueous humor
`through the ciliary muscle during prostaglandin treatment has
`been studied in detail at the cellular level by Lindsey et al.41– 47
`PGF2a seems to increase the expression of c-Fos in human
`ciliary muscle cells, which in turn may increase the expression
`of matrix metalloproteinases (MMPs)—for example, MMP-1,
`MMP-2, MMP-9 and MMP-10 —as well as their precursors,42,43
`thereby perturbing the balance in the turnover of extracellular
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`1138
`
`Stjernschantz
`
`IOVS, May 2001, Vol. 42, No. 6
`
`TABLE 3. Potency Based on EC50 Values and Estimated Efficacy of PGF2a, 17-Phenyl-18,19,20-trinor-PGF2a (17-Phenyl-PGF2a), and Latanoprost
`Acid as Measured in Functional Receptor Assays24
`
`FP
`
`EP1
`
`EP2
`
`EP3
`
`IP/DP
`
`TP
`
`Prostaglandin
`Analogue
`
`Potency
`
`Efficacy
`
`Potency
`
`Efficacy
`
`Potency
`
`Efficacy
`
`Potency
`
`Efficacy Potency Efficacy
`
`Potency
`
`Efficacy
`
`1.2 3 1028
`PGF2a
`17-Phenyl-PGF2a 4.5 3 1029
`1.0 3 1028
`Latanoprost acid
`
`100
`100
`100
`
`3.2 3 1027
`6.5 3 1027
`5.0 3 1026
`
`100
`100
`100
`
`6.4 3 1026
`.1024
`.1024
`
`100
`0
`0
`
`1.6 3 1027
`.1024
`2.8 3 1025
`
`100
`0
`;80
`
`.1024
`.1024
`.1024
`
`0
`0
`0
`
`.1024
`3.4 3 1025
`.1024
`
`;20
`;50
`0
`
`The receptor assays were based on the following tissues: FP, cat iris sphincter; EP1, bovine iris sphincter in the presence of GR32191B; EP2,
`electrical stimulation of guinea pig ileum; EP3, electrical stimulation of guinea pig vas deferens; IP/DP, prevention of adenosine diphosphate-
`induced guinea pig platelet aggregation; and TP, guinea pig platelet aggregation. For estimation of efficacy, the compounds were compared with
`PGF2a (FP), PGE2 (EP1, EP2, and EP3), carbaprostacyclin (IP), BW245C (DP), and U-46619 (TP). Potency is expressed in moles per liter and efficacy
`as percentage.
`
`matrix components toward catabolism.44 – 46 PGF2a-IE was
`found to reduce collagens I, III, and IV in the ciliary muscle and
`adjacent sclera of the monkey after topical treatment with 2 mg
`twice daily for 5 days.47 Similar results were obtained by
`Ocklind48 who demonstrated a decrease in collagens I, III, and
`IV; laminin; fibronectin; and hyaluronan in human ciliary mus-
`cle cell cultures exposed to latanoprost acid in parallel with an
`increase in MMP-2 and MMP-3. She also found evidence for
`reduced collagens IV and VI levels in the ciliary muscle after 10
`days of topical treatment with 3 mg latanoprost daily in mon-
`keys.48 Furthermore, evidence for a change in the shape of
`ciliary muscle cells was also found after exposure to latano-
`prost acid in vitro, with alterations in the actin and vinculin
`localization in the cells.39 Thus, the results indicate that latano-
`prost may have complex effects on ciliary muscle, the net
`effect being increased percolation of aqueous humor through
`the tissue.
`
`Vascular Effects of Latanoprost
`Both the local and systemic vascular effects of latanoprost have
`been studied in detail. In the rabbit eye latanoprost induced no
`or minimal change in blood flow,19 in sharp contrast to PGF2a-
`IE, which induced marked increase in blood flow to the surface
`structures and the anterior uvea after topical application.49 The
`hyperemic effect of PGF2a-IE seems to be based on a release of
`nitric oxide (NO), and apparently the mechanism leading to
`NO release does not involve FP receptors.49 Of interest, sen-
`
`sory denervation by electrocoagulation of the ophthalmic
`nerve, almost completely abolished the hyperemic effect of
`PGF2a-IE in rabbits, implying that the effect is nerve-medi-
`ated.50 This fits well with the absence of nociceptive effect of
`FP prostanoid receptor agonists such as latanoprost. By using
`selective agonists we studied which of the prostanoid recep-
`tors mediate the nociceptive response to prostaglandins in the
`cat eye and found that the FP and EP2 receptors are of little or
`no importance (Fig. 3). Stimulation of the DP, IP, EP1, and EP3
`receptors, on the contrary, induced a nociceptive response in
`the cat eye (Fig. 3). Whether PGF2a-IE–induced conjunctival
`hyperemia in humans also involves sensory nerves is unknown,
`but it is quite possible.
`Latanoprost and PhXA34 tested at a dose of approximately
`four times the clinical dose of latanoprost in Xalatan had a
`negligible effect on the regional blood flow in the monkey eye
`after topical application.51 Neither was any effect seen on
`capillary permeability to albumin in the monkey eye.51 Intra-
`venous injection of latanoprost in escalating doses of up to 6
`mg/kg body weight had no statistically significant effect on the
`uveal or retinal blood flow in monkeys, although a tendency
`toward increased blood flow was observed (Table 4).19 In
`aphakic monkey eyes with intact posterior lens capsule, latano-
`prost induced no capillary leakage in the retina as studied with
`fluorescein angiography during 6 months of treatment, and
`similar results were also obtained during shorter treatment
`periods in pseudophakic patients.52 Thus, it appears that the
`
`FIGURE 3. Maximum nociceptive effect of selective prostanoid receptor agonists in the cat eye. The
`agonists were applied unilaterally at three different doses. The irritation was estimated by observing the
`animals for 6 hours after administration of the test substances. An arbitrary scale of 0 to 3 was used: 0, no
`signs of ocular irritation; 1, slight; 2, moderate; and 3, marked signs of irritation as evident from complete
`lid closure and lacrimation. The complete name of the EP3 agonist is 13,14-dihydro-D14-trans-15-deoxy-
`17-phenyl-18,19,20-trinor-PGF2a-IE, and the compound is not a full agonist on the EP3 receptor. Thus, the
`effect on the EP3 receptor may be underestimated. Mean 6 SEM; n 5 4 – 6 for each compound and dose;
`*P , 0.01, paired t-test. IE, isopropyl ester; ME, methyl ester.
`
`Downloaded From: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933221/ on 05/11/2017
`
`Micro Labs Exhibit 1010-5
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`

`

`IOVS, May 2001, Vol. 42, No. 6
`
`The Proctor Lecture
`
`1139
`
`TABLE 4. Effect of Intravenous Injection of Escalating Doses of Latanoprost on the Blood Flow in the Monkey Eye and Vital Organs
`as Studied with Radioactively Labeled Microspheres19
`
`Baseline
`
`0.6 mg/kg
`
`2 mg/kg
`
`6 mg/kg
`
`Ocular tissues
`Retina
`Choroid
`Ciliary body
`Iris
`
`Other tissues
`Frontal brain
`Occipital brain
`Parietal brain
`Cerebellum
`Choroid plexus
`Myocardium right atrium
`Myocardium left atrium
`Myocardium right ventricle
`Myocardium left ventricle
`Liver
`Stomach
`Ileum
`Colon
`Kidney
`
`27 6 3
`570 6 95
`80 6 14
`12 6 2
`
`0.66 6 0.06
`1.64 6 0.34
`0.56 6 0.06
`0.54 6 0.07
`5.02 6 0.54
`0.40 6 0.09
`0.44 6 0.11
`1.35 6 0.18
`1.90 6 0.21
`0.26 6 0.05
`0.24 6 0.04
`0.82 6 0.14
`0.55 6 0.10
`5.80 6 0.58
`
`25 6 4
`574 6 92
`83 6 12
`13 6 2
`
`0.70 6 0.07
`1.73 6 0.36
`0.59 6 0.07
`0.50 6 0.05
`4.94 6 0.38
`0.42 6 0.06
`0.47 6 0.11
`1.58 6 0.18
`2.10 6 0.18
`0.26 6 0.05
`0.24 6 0.04
`0.89 6 0.14
`0.56 6 0.07
`5.53 6 0.45
`
`30 6 3
`670 6 119
`103 6 19
`12 6 2
`
`0.81 6 0.09
`2.00 6 0.50
`0.68 6 0.10
`0.55 6 0.05
`5.59 6 0.60
`0.73 6 0.20*
`0.60 6 0.17
`2.28 6 0.38
`2.79 6 0.46
`0.32 6 0.12
`0.21 6 0.03
`0.93 6 0.13
`0.55 6 0.11
`5.42 6 0.42
`
`40 6 4
`669 6 99
`105 6 16
`15 6 2
`
`1.09 6 0.16*
`1.69 6 0.29
`0.88 6 0.13*
`0.61 6 0.08
`6.06 6 0.70
`1.29 6 0.29*
`0.89 6 0.22*
`4.68 6 1.10*
`4.73 6 1.01*
`0.26 6 0.08
`0.40 6 0.10
`1.36 6 0.23*
`0.60 6 0.06
`5.93 6 0.42
`
`The blood flow in the eye is expressed per whole tissue and represents the right eye. Eye tissue data are in milligrams per minute; other tissue
`data are in grams per minute per gram tissue weight. (Mean 6 SEM; n 5 5–7.)
`* P , 0.05 compared with baseline (ANOVA; Tukey’s test).
`
`FP receptor, if expressed in the vasculature, plays no or only a
`limited role in the regulation of vessel tone and capillary
`permeability in the eye.
`The effects of latanoprost on the systemic circulation have
`been studied in monkeys after intravenous administration.
`With escalating doses of up to 6 mg/kg body weight an increase
`of the blood flow in parts of the brain as well as the heart was
`found, whereas very little effect was seen in other vital organs,
`such as the liver, gastrointestinal tract, and kidneys (Table 4).
`A tendency toward a slight increase in blood pressure was
`found. This effect seems to be based on increased cardiac
`output induced by high doses of the drug in anesthetized
`animals.19 It should be emphasized that the highest dose of 6
`mg/kg body weight is approximately 100 times the clinical
`dose of latanoprost in Xalatan (per body weight) applied top-
`ically on the eye.
`
`Effects of Latanoprost on the Respiratory System
`As PGF2a is a well-known constrictor of human bronchi,53–56
`the effect of latanoprost on pulmonary function in healthy
`volunteers and patients who have bronchial asthma was im-
`portant to investigate. No negative effects on pulmonary func-
`tion were observed in two specially designed clinical stud-
`ies.57,58 In monkeys, however, intravenous infusion of high
`doses of latanoprost was found to increase the intrathoracic
`inspiration– expiration pressure difference consistent with
`bronchoconstriction (unpublished results; Pharmacia). A study
`was therefore undertaken to determine the effects of latano-
`prost acid on human bronchioles in vitro. Both PGF2a and
`latanoprost acid contracted the smooth muscle of the bronchi-
`oles, as measured in small-vessel myographs with an EC50 value
`of approximately 1026 M. Latanoprost acid exerted about half
`the maximum effect of PGF2a.59 Both the contraction to PGF2a
`and latanoprost acid was completely abolished by a TP recep-
`tor antagonist (GR32191B). Thus, it appears that the effect is
`mediated primarily by TP receptors and not FP receptors. A
`concentration of 1027 M was necessary to elicit any response
`at all to latanoprost acid.59 This concentration exceeds the
`maximum concentration in