Advanced Drug Delivery Reviews 61 (2009) 1427–1449
`
`Contents lists available at ScienceDirect
`
`Advanced Drug Delivery Reviews
`
`j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / a d d r
`
`Safety and efficacy of sodium caprate in promoting oral drug absorption: from in
`vitro to the clinic
`Sam Maher a,b, Thomas W. Leonard c, Jette Jacobsen d, David J. Brayden a,b,⁎
`a UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland
`b UCD Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland
`c Merrion Pharmaceuticals, 3200 Lakedrive, City West Business Campus, Dublin 24, Ireland
`d Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Denmark
`
`a r t i c l e
`
`i n f o
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`a b s t r a c t
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`Article history:
`Received 7 August 2009
`Accepted 24 September 2009
`Available online 1 October 2009
`
`Keywords:
`Oral drug delivery
`Sodium caprate (C10)
`Absorption promoter
`Drug delivery platforms
`Clinical trials
`Oral formulation
`Drug delivery systems
`
`Contents
`
`A major challenge in oral drug delivery is the development of novel dosage forms to promote absorption of
`poorly permeable drugs across the intestinal epithelium. To date, no absorption promoter has been approved
`in a formulation specifically designed for oral delivery of Class III molecules. Promoters that are designated safe
`for human consumption have been licensed for use in a recently approved buccal insulin spray delivery system
`and also for many years as part of an ampicillin rectal suppository. Unlike buccal and rectal delivery, oral
`formulations containing absorption promoters have the additional technical hurdle whereby the promoter and
`payload must be co-released in high concentrations at the small intestinal epithelium in order to generate
`significant but rapidly reversible increases in permeability. An advanced promoter in the clinic is the medium
`chain fatty acid (MCFA), sodium caprate (C10), a compound already approved as a food additive. We discuss
`how it has evolved to a matrix tablet format suitable for administration to humans under the headings of
`mechanism of action at the cellular and tissue level as well as in vitro and in vivo efficacy and safety studies. In
`specific clinical examples, we review how C10-based formulations are being tested for oral delivery of
`bisphosphonates using Gastro Intestinal Permeation Enhancement Technology, GIPET® (Merrion Pharma-
`ceuticals, Ireland) and in a related solid dose format for antisense oligonucleotides (ISIS Pharmaceuticals, USA).
`© 2009 Elsevier B.V. All rights reserved.
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`1.
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`2.
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`Introduction .
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`1.1.
`Alternative approaches to delivery of poorly permeable drugs .
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`1.2.
`Intestinal absorption promoters .
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`C10 .
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`Intestinal absorption-promoting capacity of C10: Cultured human intestinal epithelial monolayers, isolated intestinal mucosae
`2.1.
`and animal models .
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`2.2. Mechanism of C10 permeability enhancement across intestinal epithelia.
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`2.2.1.
`Paracellular mode of action studies
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`Physicochemical properties of C10 in solution .
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`2.2.2.
`2.2.3.
`Transcellular mode of action studies .
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`Preclinical safety data for C10.
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`2.3.
`Promoting activity and safety of C10 in man .
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`Case study I: Rectal delivery of ampicillin using C10 .
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`3.1.
`Case study II: Oral delivery of oligonucleotides using C10.
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`3.2.
`Case study III: GIPET®, oral formulations of poorly permeable drugs with C10 .
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`3.3.
`Perspective on the safe and effective use of C10 in oral drug delivery .
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`4.
`Conclusions .
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`5.
`Acknowledgements and disclosure .
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`References .
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`. 1428
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`⁎ Corresponding author. UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland. Tel.: +353 1 7166013; fax: +353 1
`7166219.
`E-mail address: david.brayden@ucd.ie (D.J. Brayden).
`
`0169-409X/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
`doi:10.1016/j.addr.2009.09.006
`
`Grün. Exhibit 1086
`Grünenthal v. Antecip
`PGR2017-00022
`
`

`

`1428
`
`1. Introduction
`
`S. Maher et al. / Advanced Drug Delivery Reviews 61 (2009) 1427–1449
`
`The number of drugs emerging from R & D programmes as lead
`candidates that are poorly absorbed following oral administration is
`increasing, the majority of which are delivered by injection at
`considerable patient inconvenience. Biotech drugs represent a growing
`proportion of drugs in preclinical development and these have
`inherently low oral bioavailability (F) [1]. The delivery route has a
`significant impact on the commercial success of therapeutics for long-
`term indications and the potential market of selected biotech drugs may
`not be maximized due to the requirement for repeated injections [2,3].
`Nasal formulations have largely superseded sub-cutaneous (s.c.)
`injections for the peptide calcitonin, but there are still issues of rhinitis
`and local tolerance that reduce patient compliance and hence an oral
`delivery system would be preferable [4]. In addition, the first pulmonary
`formulation of insulin (Exubera®, Pfizer Ltd, USA) was withdrawn due
`to poor patient uptake, possible side effects, an unattractive device and a
`concomitant requirement for insulin injections [5]. One of the major
`challenges in biopharmaceutical development therefore continues to be
`the need for effective oral delivery systems.
`The biopharmaceutics classification system (BSC) categorizes
`soluble drugs with poor intestinal permeability as Class III drugs [6].
`Candidates comprise peptides, proteins, nucleic acid therapeutics and
`polysaccharides as well as some conventional organic molecules.
`Unlike most lipophilic agents, hydrophilic molecules are generally not
`passively absorbed across intestinal epithelia, largely due to restricted
`permeation across brush border membranes (Fig. 1). Absorptive flux
`of small hydrophilic molecules including valacyclovir, bestatin and
`cephalexin may occur to some extent either via carrier-mediated
`transporters on epithelial cell apical membranes (primarily the
`human oligopeptide transporter-1 (hPEPT1) [7]) or alternatively by
`paracellular flux via tight junctions (TJs) [8]. TJs form a barrier to the
`uncontrolled absorption of noxious luminal antigens (gate function),
`and maintain epithelial polarity (fence function) [8,9]. In general, the
`TJ consists of a restrictive pathway (shunt) with a sharp molecular
`size cut off, and a second unrestrictive pathway (small pore) that
`permits paracellular permeation of molecules of radii <4.0 Å [10,11].
`Depending on the intestinal region, TJ pore radii range from 3 to 11 Å,
`sufficient to permit mannitol (radius 3.3 Å) and EDTA (5.4 Å) to
`permeate to an extent, whereas the passage of inulin (10–20 Å) and
`fluorescent-dextran 4 kDa (FD4, 13 Å) is minimal [12–16].
`A number of approaches have been used to promote oral delivery of
`Class III drugs (Fig. 1). One of the simplest approaches to increasing
`oral F is the use of intestinal absorption promoters. Study of absorption
`promoters began in the 1960s when ethylenediaminetetraacetic acid
`(EDTA) was shown to increase absorption of heparin in rats and dogs
`[17]. Since then, there are numerous reports of epithelial-permeating
`activity by a number of dietary agents, surfactants and polymers, some
`of which have achieved ‘generally recognized as safe’ (GRAS) status as
`food additives. Recently, more sophisticated TJ modulators have
`emerged from in vitro and preclinical studies arising from a greater
`understanding of the structure and function of TJs [18–20]. The
`candidate molecules that are to be delivered orally using absorption
`promoters should have a sufficiently wide therapeutic index in order
`to cater for the increased variance in oral F between individual subjects
`seen in clinical studies. It is also of benefit if the drug is relatively
`inexpensive and is of high potency since oral absorption will be
`significantly reduced when co-formulated with even the most
`promising delivery technology. To date however, there are only a
`selected number of intestinal promoters licensed as excipients in the
`delivery of poorly-absorbed drugs. While most of these approved
`excipients were designed to improve solubility, some were subse-
`quently discovered to increase transcellular permeability (e.g. macro-
`gol-8 glyceride (Labrasol®, Gattefosse Corp., France [21]). Registration
`of products containing enhancers has however, not occurred to the
`extent that one might expect, given the many convincing in vitro and
`
`Fig. 1. (a) Schematic representation of drug delivery systems that have been shown to
`increase transmucosal drug permeability. (1) Most oral drugs with the desired
`solubility are normally absorbed passively by transcellular path without the need for a
`drug delivery system, (2) carrier-mediated prodrug formulation (e.g. valaciclovir)
`(3) modified solubility prodrug formulation (e.g. enalapril), (4) absorption promoters
`can increase permeability by paracellular permeability and/or by transcellular
`perturbation (e.g. C10) (5) receptor mediated nanoparticle endocytosis (e.g. vitamin
`B12) and (6) carrier-based drug delivery systems (e.g. Eligen®, Emisphere, USA) (b)
`EM of a cross section of the human colonic mucosa with intact transcellular and
`paracellular barriers. Single white arrow head denotes tight junction. Vertical bar
`denotes 2 µm.
`
`preclinical reports. Some valid concerns about the development of
`enhancer-containing products relate to the known intestinal epithelial
`toxicity induced by many promoters (e.g. surfactants, EDTA, bacterial-
`derived toxins), while unresolved issues pertain to the potential for
`by-stander pathogen and toxin absorption through reversible weak-
`ening of the gut barrier on a repeated basis.
`The medium chain fatty acid (MCFA) promoter, sodium caprate
`(C10), is both a food additive and a component of a rectal suppository
`originally marketed in Sweden (Doktacillin®, Meda, Solna, formerly
`marketed by AstraZeneca, Södertälje [22]) and in Japan (Kyoto
`Pharmaceutical Industries, Ltd, Kyoto [23]). It is currently in clinical
`trials as a key component of several proprietary oral formulations
`[24–26]. The nature of its mechanism of action, efficacy, and the
`possibility of inducing toxicity are of primary interest in commercial-
`ization of formulations based on this technology. Here, we focus on
`the development and current status of C10 in formulations designed to
`increase oral F in the context of other absorption-promoting
`technologies and alternative approaches.
`
`

`

`S. Maher et al. / Advanced Drug Delivery Reviews 61 (2009) 1427–1449
`
`1429
`
`1.1. Alternative approaches to delivery of poorly permeable drugs
`
`There are currently only two peptides licensed for use by the oral
`route: cyclosporin and desmopressin. Cyclosporin (Neoral®, Novartis,
`Switzerland) is delivered in a solubilising micro-emulsion with an oral
`F of approximately 30%. This high F can be explained in part by the
`unique physicochemical characteristics of the cyclic undecapeptide
`[27]. Desmopressin (DDAVP®, Sanofi-Aventis, France) is a potent
`vasopressin analogue that is also delivered orally, despite its very low
`oral F (0.1%) [28]. Successful approaches to overcoming poor
`intestinal permeability have also focused on prodrugs, inactive drug
`precursors with greater permeability across the intestinal epithelium
`than the active [7,29–31]. Once absorbed across the intestinal
`epithelium, the prodrug is hydrolytically or enzymatically converted
`to active drug. The most common prodrugs have a moiety that
`increase drug lipophilicity thereby promoting passive transcellular
`diffusion (e.g. enalapril, pivampicillin) or a recognition ligand that
`enables the drug to be shuttled across the epithelium on an epithelial
`transporter (e.g. hPEPT1 for valaciclovir and midodrine) (Fig. 1).
`Although prodrugs have been effective for small organic drugs and
`some short chain peptides to date, it has been less successful for
`macromolecules and longer chain peptides.
`Conjugating biotech drugs to polymers that increase transmucosal
`permeability and stability is also a useful approach. Fatty acid
`conjugates of peptides and proteins have been synthesised and they
`demonstrate improved oral absorption and stability [32]. Such
`conjugates include insulin [33], calcitonin [34], leucine enkephalin
`analogue (DADLE) [35], tetragastrin [36] and phenylalanylglycine
`[37,38]. Furthermore, site-specific PEGylation to the lysine-18 of
`salmon calcitonin (sCT) increased peptide stability and led to
`decreased serum calcium levels upon intra-duodenal instillation in
`rats [39]. Biotinylation of sCT has been shown to increase transmu-
`cosal flux across Caco-2 monolayers through targeting of apical
`membrane biotin receptors [40]. An alkylated, PEGylated, amphiphilic
`insulin conjugate (HIM-2, Biocon Corp., India) increased oral F of
`insulin in dogs [41] and has reached Phase II clinical studies [42]. An
`orally-administered amphiphilic calcitonin conjugate is also under
`investigation using similar technology [43]. Conjugation of insulin to
`vitamin B12 for receptor-mediated delivery can also lead to increased
`absorption of insulin in diabetic rats [44], although there are receptor
`capacity-related issues that may ultimately limit efficacy in man.
`Despite encouraging data from peptide conjugations, direct
`chemical modification is molecule-specific. An attractive alternative
`is the use of oral drug delivery platforms that do not involve new
`chemical entities and which can be fine-tuned to apply to a range of
`poorly permeable drugs. Mucoadhesive polymers that prolong the
`contact time between drug and the intestinal epithelium can create a
`steep concentration gradient to drive passive absorption [45,46].
`Thiomers are an interesting group of mucoadhesives that have shown
`promise in animal models. For example, improved oral F for low
`molecular weight heparin (LMWH) and insulin has been achieved in
`rodents with thiolated polycarbophil formulations [47,48]. Use of
`mucoadhesives in the gastrointestinal (GI) tract may, however, be
`problematic because of the high rate of mucus turnover and the large
`amount of competing mucus in the lumen [46,49].
`In contrast,
`mucoadhesion has been successfully employed in buccal delivery
`systems including glyceryl trinitrate (Suscard®, Forest Laboratories,
`USA) and miconazole (Lauriad®, BioAlliance Pharma, France) [50].
`Alternatively, the use of nanoparticles comprising biocompatible
`polymers (e.g. chitosan, polylactide-co-glycolide, starch and glucans)
`can protect cargoes from GI proteases, increase GI retention and
`promote absorption across gut associated lymphoid tissue (GALT)
`and, to a lesser extent, enterocytes [51–53]. Most data on nanoparticle
`absorption from rodent models suggest that M cells in the follicle-
`associated epithelium of Peyer's patches (PP) are the favored site of
`uptake for particles of diameter 500–1000 nm [51]. Given the paucity
`
`of M cells in the GI tract of adults, the relevance of PP uptake remains
`controversial and, for example, convincing oral vaccine data using
`nanoparticles in man is lacking [54,55]. Recent in vitro data suggests
`that particle uptake by enterocytes can be increased if interaction
`with the mucous layer can be overcome using a coating of low
`molecular weight ‘non-stick’ PEG [56], the opposite to mucoadhesion.
`Targeted nanoparticles can be created by attaching surface ligands to
`stimulate receptor-mediated transport of particle-entrapped payload
`and, unlike the direct ‘payload conjugation-to-ligand’ approach, this
`may have greater potential to deliver a greater ratio of drug per
`transporter to compensate for lower receptor numbers or transport
`capacity [57]. Targeted particle systems for oral delivery unfortunately
`require complex synthetic and manufacturing processes and rely on
`unpredictable translation of data from rodent models to man in respect
`of differences in GI physiology and variable receptor expression. Simpler
`mixing and blending nano-particulate drug formats have, however,
`been very successful in oral delivery of insoluble Class II drugs (e.g.
`NanoCrystal®, Elan, Ireland) [58], where permeability is not the issue. It
`is possible that this technology may also be modified for poorly
`permeable peptides since there are surfactants which can be adapted
`into the process [59].
`
`1.2. Intestinal absorption promoters
`
`A large number of well-known substances have been shown to
`alter intestinal permeability ranging from spices and fatty foods
`[60,61], alcohol [62] and drugs [63], to bacterial toxins [64]. Increased
`intestinal permeability is also associated with inflammatory bowel
`disease [65] and strenuous exercise [66]. The majority of absorption
`promoters tested in cultured intestinal epithelial models have not
`however, been tested in man due to inherent toxicity. In any case, few
`drug delivery platforms (of which oral absorption promoters are a
`subset) have advanced to clinical evaluation [67]. Amongst initial
`preclinical investigations of agents that did not proceed to the clinic
`are the macrocyclic fungal metabolites, cytochalasins, which increase
`paracellular permeability through contraction of the perijunctional
`ring of actin and myosin II (PAMR) causing displacement of TJ proteins
`[68]. Other failed candidates include the calcium chelator, ethylene
`glycol tetraacetic acid (EGTA); it increases gut permeability via
`myosin light chain kinase (MLCK)-dependent dilation of the PAMR
`[69]. Similarly, detergent surfactants including sodium dodecyl sulfate
`(SDS) and Triton X-100 increase transmucosal drug absorption by
`destruction of the mucosal surface and exfoliation of epithelia [70]
`and therefore, could not be progressed.
`Microbial toxins also increase paracellular permeability across
`intestinal epithelial TJs, although they are unlikely to be safe
`candidates for oral drug delivery in their native form. Examples
`include Zonula occludens toxin (Zot), a virulence factor in diarrhea
`associated with strains of Vibrio cholera [64] and the Clostridium
`perfringens enterotoxin (CPE), which can cause necrosis and desqua-
`mation of the epithelial surface of human ileal mucosae [71].
`Structural analogues of Zot and CPE are members of a new generation
`of promoters that target TJ proteins [18–20,72–74]. A review of the
`patent literature reveals a vast number of peptide-based promoters
`that also target the paracellular pathway [20]. These promoters offer
`greater specificity for the TJ and may offer reduced cytotoxicity
`compared to many surfactants, but their safety and efficacy in man has
`yet to be established.
`Importantly,
`it is not yet clear whether
`transiently-modulating TJs to increase drug absorption (in the
`absence of effects on the transcellular pathway) will increase oral F
`to an acceptable level
`in man, since the paracellular pathway
`comprises only 0.1% of the surface area of the intestinal epithelium,
`but it may still be a relevant permeation route for delivering selected
`potent low molecular weight molecules.
`One of the most advanced carrier technologies in clinical trials
`based on absorption–promotion is Eligen® (Emisphere Technologies,
`
`

`

`1430
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`S. Maher et al. / Advanced Drug Delivery Reviews 61 (2009) 1427–1449
`
`NJ, USA). The proposed mechanism for these delivery agents is that
`they increase transcellular drug absorption via non-covalent linkage
`to the carrier [75], although there is ongoing controversy over the
`thermodynamic aspects of the interaction. An acetylated amino acid
`carrier, N-[8]-(2-hydroxybenzoyl)amino] caprylate (SNAC), increased
`oral F of a range of poorly permeable cargoes in human studies [2,75–
`80]. SNAC has recently achieved provisional GRAS status as a food
`additive with no overt toxicity detected in Sprague–Dawley rats at a
`dose of 1 g/kg/day for 10–13 weeks [81]. Issues for SNAC and other
`absorption promoter technologies that must be addressed are large
`intra-subject variability in efficacy, the large ratio of carrier: active,
`and the high dosing frequency that is currently required. A number of
`oral peptide proprietary formulations are also in the clinic based on
`enteric-coated capsules containing promoters that are GRAS excipi-
`ents (Axcess™ Technology, Bone Medical, Australia [82]). This
`platform has been used to deliver insulin (Capsulin®) and calcitonin
`(Capsitonin®) in separate Phase II clinical studies. Hydroance
`Technology™ by Lipocine Inc (USA) has constituents including a
`controlled release system with bile acid/salt and a mixture of
`hydrophilic and hydrophobic surfactants [83]. Preclinical studies
`with this formulation in rat, porcine, and primate models demon-
`strated increased absorption of both LMWH (5 kDa) and a peptide
`hormone (3.5 kDa). On the polymer side, soluble trimethylated
`chitosan appears to be a promising absorption promoter and/or
`vaccine adjuvant in preclinical research as it could offer peptide
`protection and aid permeation when presented in a particle format
`(reviewed [48,84–86]). Approved in some markets, albeit for buccal
`delivery, is Oralin® (Generex Biotech, Canada), a formulation for the
`delivery of insulin which promotes absorption via a microfine mixed
`micelle spray containing GRAS surfactants and bile salts (RapidMist®,
`Generex Biotech, Canada) [87].
`
`2. C10
`
`C10 is the sodium salt of the aliphatic saturated 10-carbon MCFA,
`capric acid, also known as sodium decanoate (or the sodium salt of
`decanoic acid). Capric acid is present in dairy products, particularly
`milk, where it constitutes a significant proportion of the fatty acid
`content. Percentage levels of the total
`fatty acid content in
`mammalian milk are: trace amounts in rats, 1–3% in humans and
`cows, 9% in sheep, 8% in goats and 20% in rabbits [88,89]. The
`approximate concentration of capric acid in human and cow milk can
`therefore be estimated to be as high as 0.2 mM [89,90]. Importantly,
`this concentration is still 50-to-1000 fold lower than that required to
`increase drug permeability. Capric acid is also present in a number of
`oils including coconut oil (4.5–9.7%), palm kernel oil (7–14%), bay tree
`oil (37%) and elm seed oil (50%) [88]. The lethal dose, 50% (LD50) of
`capric acid following acute oral gavage to rats was 3.7 g/kg [91,92].
`Importantly, long-term dietary exposure of rats to capric acid in rice
`(100 g/kg rice) with an approximate daily intake of 500 mg/kg rat
`weight for 150 days resulted in no observable changes in stomach
`morphology [93]. C10 is approved by the FDA as a direct food additive
`for human consumption [94,95]. Furthermore, when reviewed by the
`FAO/WHO Joint Expert Committee on Food Additives, C10 was not
`limited to a specific allowable daily intake because it was judged that
`its presence in food would have no impact on human health [94,95].
`
`Intestinal absorption-promoting capacity of C10: Cultured human
`2.1.
`intestinal epithelial monolayers, isolated intestinal mucosae and animal
`models
`
`The ability of C10 to facilitate rectal absorption was first discovered
`over 25 years ago [96–98]. Rectal
`formulations containing C10
`increased the absorption of a range of β-lactam antibiotics in rodent,
`dog and human studies [96,99]. Since the initial studies of rectally-
`administered C10 in 1982, the promoter has since been assessed
`
`extensively with a wide range of co-administered poorly permeable
`drugs in every accepted intestinal delivery screening system. These
`include intestinal epithelial cell monolayers (Table 1), isolated animal
`and human intestinal mucosae (Table 2), in situ gut perfusions and
`intestinal instillations (Table 3), and extensive animal (Table 3) and
`human studies (Table 4). The increase in drug absorption observed
`with C10 can be dependent on the assessment model used. For
`example, delivery of the same test solution in three different rat
`models demonstrated an enhancement in the following order: jejunal
`closed loop (anesthetized) > intestinal instillation (anesthetized) >
`catheter intubation to conscious rats (personal communication,
`Tillman L.G.,
`ISIS Pharmaceuticals, USA).
`In vivo model-specific
`variables include the type of surgery, extent of tissue damage, the
`damage/repair cascade, the type and rate of delivery of anesthetic and
`
`Table 1
`Permeating-enhancement properties of C10 in Caco-2 monolayers.
`
`Marker/drug
`
`C10 (mM)
`
`Enhancement ratio
`
`<1a
`Clodronate
`10
`Mannitol
`0.75
`1
`15a
`Mannitol
`13
`1.3a
`Mannitol
`5
`1a
`Mannitol
`10
`6.3a
`Mannitol
`10
`Mannitol
`13
`9
`Mannitol
`13
`12
`Mannitol
`10
`8
`Mannitol
`16
`7.7
`5a
`Mannitol
`10
`66a
`Mannitol
`50
`64a
`Mannitol
`50
`3a
`Decapeptide
`25
`20a
`Atenolol
`13
`>13a
`Danshensu
`13
`>40a
`Salvianolic acid B
`13
`>10a
`Lucifer yellow
`5
`Ardeparin
`13
`7.3
`10.6a
`rhEGF
`50
`Fluorescein
`5
`1.4
`2.7a
`Fluorescein
`10
`3a
`Fluorescein
`13
`FD4
`5
`0.9
`>10a
`FD4
`5
`FD4
`1
`1.7
`16.5a
`FD4
`10
`3a
`FD4
`10
`FD4
`10
`6.5
`10.6a
`FD4
`10
`6a
`FD4
`13
`5.5a
`FD4
`13
`FD4
`13
`37
`4.3a
`FD4
`50
`>10a
`FD10
`5
`>10a
`FD20
`5
`FD20
`13
`56
`>10a
`FD40
`5
`2.3a
`Acamprosate
`16
`4.6a
`Rhodamine
`10
`70a
`Inulin
`50
`>10a
`PEG 900
`25
`17a
`Cyclopeptide
`10
`Penicillin G
`13–16
`–
`Penicillin V
`10
`>2
`Penicillin V
`10
`8.5
`Penicillin V
`10
`16
`20a
`Cimetidine
`50
`2.3a
`Heparin
`10
`Vasopressin
`13
`10
`1.4a
`Epirubicin
`10
`PEG 326
`10
`5
`PEG 546
`10
`17
`Streptokinase
`10–20
`>50
`PEG 4000
`13
`3.5
`a Drop in TEER across monolayers treated with C10.
`
`Ref.
`
`[253]
`[254]
`[103]
`[153]
`[253]
`[155]
`[255]
`[114]
`[152]
`[256]
`[175]
`[106]
`[102]
`[106]
`[257]
`[257]
`[257]
`[153]
`[255]
`[102]
`[164]
`[258]
`[104]
`[164]
`[153]
`[108]
`[258]
`[168]
`[259]
`[193]
`[165]
`[161]
`[114]
`[260]
`[153]
`[153]
`[114]
`[153]
`[256]
`[258]
`[102]
`[106]
`[193]
`[103]
`[198]
`[155]
`[100]
`[102]
`[101]
`[114]
`[171]
`[114]
`[114]
`[196]
`[261]
`
`

`

`Table 2
`Permeating–enhancing properties of C10 using ex vivo models of the GI tract.
`
`S. Maher et al. / Advanced Drug Delivery Reviews 61 (2009) 1427–1449
`
`1431
`
`Species
`
`Intestinal region
`
`Mouse
`Colon
`Rat
`Stomach
`Rat
`Duodenum
`Rat
`Jejunum
`Rat
`Jejunum
`Rat
`Jejunum
`Rat
`Jejunum
`Rat
`Jejunum
`Rat
`Jejunum
`Rat
`Jejunum
`Rat
`Ileum
`Rat
`Ileum
`Rat
`Ileum
`Rat
`Ileum
`Rat
`Ileum
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Colon
`Rat
`Rectum
`Rabbit
`Jejunum
`Rabbit
`Jejunum
`Rabbit
`Jejunum
`Rabbit
`Colon
`Human
`Ileum
`Human
`Colon
`Human
`Colon
`Human
`Colon
`Human
`Colon
`Human
`Colon
`a Drop in TEER across mucosae treated with C10.
`
`Model
`
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Everted sac
`Everted sac
`Everted sac
`Ussing
`Ussing
`Ussing
`Ussing
`Everted sac
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Everted sac
`Franz cell
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`Ussing
`
`Marker/drug
`
`Mannitol
`Ardeparin
`Ardeparin
`Ardeparin
`Ebiratide
`Insulin
`Phenol red
`Epirubicin
`Cefotaxime
`Ceftazidime
`Ardeparin
`Mannitol
`EDTA
`Poly-sucrose
`Epirubicin
`Ardeparin
`Insulin
`Phenol red
`Phenol red
`Ebiratide
`Mannitol
`Mannitol
`Mannitol
`FD4
`FD4
`FD70
`Inulin
`Propranolol
`Inulin
`Mannitol
`Thiourea
`Gly-L-Phe
`EDTA
`Mannitol
`FD4
`FD4
`EDTA
`HRP
`
`C10 (mM)
`
`Enhancement ratio
`
`10
`13
`13
`13
`20
`20
`20
`100
`13
`13
`13
`30
`10
`10
`100
`13
`20
`20
`–
`20
`10
`10
`13
`10
`26
`10
`13
`–
`13
`13
`13
`50
`10
`10
`10
`26
`10
`10
`
`3a
`1.1
`1.3
`1.3
`1.5
`0.97
`1.1
`4.5
`4.7
`1.8
`1.3
`80
`4.5a
`10a
`2
`1.6
`2.5
`4
`7.6
`3.8
`7a
`3.9a
`11a
`25a
`31a
`44a
`>5
`1.5
`1
`1
`<1
`>2
`7a
`5a
`7a
`17a
`2a
`2a
`
`Ref.
`
`[168]
`[255]
`[255]
`[255]
`[142]
`[143]
`[109]
`[171]
`[182]
`[182]
`[255]
`[218]
`[110]
`[110]
`[171]
`[255]
`[143]
`[109]
`[262]
`[142]
`[111]
`[168]
`[11]
`[111]
`[167]
`[111]
`[199]
`[263]
`[144]
`[144]
`[144]
`[264]
`[156]
`[111]
`[111]
`[167]
`[112]
`[112]
`
`its effect on water absorption and secretion. Therefore, it is important
`to consider the limitations of the models used to evaluate C10 in order
`to make an informed assessment.
`C10 increases the flux of many different types of poorly permeable
`agents across intestinal epithelia in vitro, including antibiotics [100],
`heparin [101] and recombinant EGF [102]. The concentration of C10
`required to increase the flux of paracellular markers across Caco-2
`monolayers is 10–13 mM, close to its original reported critical micelle
`concentration (CMC) in HBSS [103,104]. In parallel, it causes a rapid
`reversible concentration-dependent reduction in transepithelial elec-
`trical resistance (TEER) values across Caco-2 monolayers (e.g.
`[103,105,106] and Table 1). The TEER values of Caco-2 monolayers
`do not recover following extended exposure periods or from higher
`concentrations of C10 [103,105,107,108]. Still, the relevance of
`exposing monolayers to C10 for long exposure times is questionable,
`since it is rapidly absorbed in vivo. Isolated intestinal mucosa mounted
`in Ussing chambers permit comparison between effects of permeation
`enhancers on different regions of the intestine, thus TEER and flux
`changes similar to that seen in Caco-2 were noted in jejunal, ileal and
`colonic mucosae from a range of species upon exposure to C10. In
`tissue mucosae, C10 decreased TEER with a concomitant increase in
`flux of poorly permeable markers including phenol red [109], poly-
`sucrose [110] and a range of FITC-dextrans [111] (Table 2). While high
`concentrations of C10 (>13 mM) invariably lead to greater enhance-
`ment of drug fluxes in Caco-2 monolayers and isolated intestinal
`mucosae (Tables 1 and 2), conclusions on mechanisms of action and
`cytotoxicity at such high concentrations are difficult to make. Similar
`to Caco-2 monolayers, the reduction in TEER caused by 10–15 mM C10
`
`in human colonic mucosae was recoverable upon washout [112], as
`were the promoting effects on paracellular flux [11].
`Despite significantly increasing permeability across in vitro and ex
`vivo intestinal models, it is worth noting that the capacity of C10 to
`increase the Papp using these models does not always permit the
`conclusion that there will be a significantly absorbed fraction in vivo.
`For example, the promoter increased the flux of FD70 across isolated
`rat colonic mucosae by 44-fold at a concentration of 10 mM, but the
`actual resulting Papp value of 10− 8 cm/s was still very low [111]. In
`colonic in situ instillations however, C10 did not increase the
`absorption of FD70 at all, even at a concentration of 100 mM [113].
`Likewise, in Caco-2 monolayers, the degree of enhancement with C10
`(10–13 mM) increased in proportion to the molecular weight (MW)
`of the associated drug [114]. For example, the Papp of [14C]-PEG (MW
`326 Da) was increased by just 5-fold over basal compared with that of
`[14C]-PEG (MW 546 Da, 17-fold). For drugs above a MW of 1200 Da,
`increased Papp values upon exposure to C10 in Caco-2 monolayers
`were not considered large enough to translate to an increased fraction
`of absorbed drug in vivo. Thus, for larger MW payloads, while the
`enhancement ratio in the presence of C10 may be higher in vitro
`because the basal flux is lower compared to molecules of lower MW, a
`large MW drug will still have poor oral F in vivo unless the
`concentration of C10 is increased significantly [106]. As a reflection
`of this, the proportion of in vivo studies that used concentrations of
`C10 above the CMC are higher than those used in vitro and ex vivo. In
`15% of studies using cell culture models, concentrations >20 mM C10
`were used to increase permeation of larger drugs (Table 1). I