Genetic and cellular toxicology of dental resin monomers

Monomers are released from dental resin materials, and thus cause adverse biological effects in mammalian cells. Cytotoxicity and genotoxicity of some of these methacrylates have been identified in a vast number of investigations during the last decade. It has been well-established that the co-monomer triethylene glycol dimethacrylate (TEGDMA) causes gene mutations in vitro. The formation of micronuclei is indicative of chromosomal damage and the induction of DNA strand breaks detected with monomers like TEGDMA and 2-hydroxyethyl methacrylate (HEMA). As a consequence of DNA damage, the mammalian cell cycle was delayed in both G1 and G2/M phases, depending on the concentrations of the monomers. Yet, the mechanisms underlying the genetic and cellular toxicology of resin monomers have remained obscure until recently. New findings indicate that increased oxidative stress results in an impairment of the cellular pro- and anti-oxidant redox balance caused by monomers. It has been demonstrated that monomers reduced the levels of the natural radical scavenger glutathione (GSH), which protects cell structures from damage caused by reactive oxygen species (ROS). Depletion of the intracellular GSH pool may then significantly contribute to cytotoxicity, because a related increase in ROS levels can activate pathways leading to apoptosis. Complementary, cytotoxic, and genotoxic effects of TEGDMA and HEMA are inhibited in the presence of ROS scavengers like N-acetylcysteine (NAC), ascorbate, and Trolox (vitamin E). Elevated intracellular levels of ROS can also activate a complex network of redox-responsive macromolecules, including redox-sensitive transcription factors like nuclear factor kappaB (NF-kappaB). It has been shown that NF-kappaB is activated probably to counteract HEMA-induced apoptosis. The induction of apoptosis by TEGDMA in human pulp cells has been associated with an inhibition of the phosphatidylinositol 3-kinase (PI3-K) cell-survival signaling pathway. Although the details of the mechanisms leading to cell death, genotoxicity, and cell-cycle delay are not completely understood, resin monomers may be able to alter the functions of the cells of the oral cavity. Pathways regulating cellular homeostasis, dentinogenesis, or tissue repair may be modified by monomers at concentrations well below those which cause acute cytotoxicity.

Diffusion of monomers from bonding resin-resin composite combinations through dentine in vitro

OBJECTIVES

Previous work has demonstrated diffusion of the monomer triethylene glycol dimethacrylate (TEGDMA) from resin composite through dentine in vitro. The objective of the present work was to examine monomer diffusion from bonding resins and resin composites used in combination.

METHODS

Occlusal cavities were prepared in tooth crowns and restored with bonding resin-resin composite combinations. Aqueous samples from the 'pulpal chamber' of each tooth were removed at timed intervals for analysis by reversed phase-high performance liquid chromatography and mass spectrometry.

RESULTS

Bonding resins contributed to monomer diffusion. A TEDGMA-containing bonding resin used in combination with a TEGDMA-containing resin composite hastened and increased TEGDMA diffusion through dentine. A 2-hydroxyethyl methacrylate (HEMA)-containing bonding resin used in combination with a TEGDMA-containing resin composite reduced TEGDMA diffusion only slightly compared with the resin composite alone and added substantial diffusion of HEMA.

CONCLUSION

The bonding resins tested contributed to monomer passage to the pulp space and did not prevent movement of monomer from resin composites to the pulp.

Molecular toxicology of substances released from resin-based dental restorative materials

Resin-based dental restorative materials are extensively used today in dentistry. However, significant concerns still remain regarding their biocompatibility. For this reason, significant scientific effort has been focused on the determination of the molecular toxicology of substances released by these biomaterials, using several tools for risk assessment, including exposure assessment, hazard identification and dose-response analysis. These studies have shown that substances released by these materials can cause significant cytotoxic and genotoxic effects, leading to irreversible disturbance of basic cellular functions. The aim of this article is to review current knowledge related to dental composites' molecular toxicology and to give implications for possible improvements concerning their biocompatibility.

Efficacy of the chemotherapeutic action of HPMA copolymer-bound doxorubicin in a solid tumor model of ovarian carcinoma

Anticancer activity and main mechanisms of action of free doxorubicin (DOX) and HPMA copolymer-bound DOX (P(GFLG)-DOX) were studied in solid tumor mice models of DOX sensitive and resistant human ovarian carcinoma. Free DOX was effective only in sensitive tumors decreasing the tumor size about three times, whereas P(GFLG)-DOX decreased the tumor size 28 and 18 times in the sensitive and resistant tumors. An enhanced accumulation of P(GFLG)-DOX in the tumor was observed, whereas only low concentrations of DOX were detected in other organs following P(GFLG)-DOX administration. This effect was dependent on the high permeability of blood vessels in untreated tumors. After treatment with P(GFLG)-DOX the permeability decreased concomitantly with the downregulation of VEGF gene expression. P(GFLG)-DOX effectively killed both types of tumors inducing apoptosis and necrosis through the activation of p53, Apaf-1, caspase 9, c-fos, or c-jun pathways, and the downregulation of the bcl-2 gene. HPMA copolymer-bound DOX preserved its activity inside cells, inhibited detoxification and defensive mechanisms encoded by GST-pi, BUDP, and HSP-70 genes, and limited DNA repair, replication, and biosynthesis by downregulation of Topo-IIalpha,beta, and TK1 genes. P(GFLG)-DOX also produced tumor tissue hypoxia and significantly activated lipid peroxidation in tumors. No damage to other organs after exposure to P(GFLG)-DOX was detectable. On the other hand, free DOX activated lipid peroxidation and led to tissue hypoxia in many organs. All data relevant to the mechanism of anticancer action of P(GFLG)-DOX indicated a higher antitumor activity and lower systemic toxicity of HPMA copolymer-bound DOX when compared with free DOX.

Enteric coated HPMC capsules designed to achieve intestinal targeting

The enteric coating of HPMC capsules containing paracetamol was investigated. Two enteric polymers, Eudragit L 30 D-55 and Eudragit FS 30 D were studied, which are designed to achieve enteric properties and colonic release, respectively. The capsules were coated in an Accela Cota 10, and, as shown by optical microscopy, resulted in capsules with a uniform coating. Scanning electron microscopy of the surface of the capsules illustrate that, in contrast to gelatin, HPMC has a rough surface, which provides for good adhesion to the coating. Dissolution studies demonstrated that capsules coated with Eudragit L 30 D-55 were gastro resistant for 2 h at pH 1.2 and capsules coated with Eudragit FS 30 D were resistant for a further 1 h at pH 6.8. The product visualisation technique of gamma scintigraphy was used to establish the in vivo disintegration properties of capsules coated with 8 mg cm(-2) Eudragit L 30 D-55 and 6 mg cm(-2) Eudragit FS 30 D. For HPMC units coated with Eudragit L 30 D-55, complete disintegration occurred predominately in the small bowel in an average time of 2.4 h post dose. For HPMC capsules coated with Eudragit FS 30 D, complete disintegration did not occur until the distal small intestine and proximal colon in an average time of 6.9 h post dose.

Preliminary clinical study of the distribution of HPMA copolymers bearing doxorubicin and galactosamine

Galactose-targeted delivery of macromolecules and drug conjugates to asialoglycoprotein receptor (ASGPR) positive cells has been widely documented in animals, although targeting in humans has never been demonstrated. In this study we report the pharmacokinetics and imaging determined in the first patient enrolled in a phase I clinical study of the poly[N-(2-hydroxypropyl)methacrylamide] copolymer bearing doxorubicin and galactosamine, known as PK2. Gradient high performance liquid chromatography (HPLC) evaluation of plasma and urine has been combined with 123I-based imaging to show biphasic clearance of the drug from the plasma (half-lives of 78+/-1 and 990+/-15), and approximately 30% delivery of the drug to the hepatic region, as determined by planar whole body imaging at 24 h. This patient has a multifocal hepatoma, and single photon emission computed tomography (SPECT) analysis showed a ratio of tumour tissue to normal liver uptake of approximately 1:3, at 24 h. On the basis of this patient, effective hepatic targeting can be achieved following an intravenous dose of 20 mg/m2 doxorubicin as PK2, however the therapeutic usefulness of this targeted drug has yet to be established.

Bioavailability of components of resin-based materials which are applied to teeth

Chemical components of many materials used in dental practice can move into the local biophase, where they can have beneficial or adverse effects. The strongest indirect evidence that components of resin-based materials used in dentistry can move into the biophase are the many reports of allergic dermatitis in dental personnel. Direct measurement of component release has shown that triethylene glycol dimethacrylate (TEGDMA), hydroxyethyl methacrylate (HEMA), and, in the case of some orthodontic cements, bis-glycidyl methacrylate and benzoyl peroxide can move into an aqueous medium from a range of resin-based materials which are applied to teeth as part of oral care. In the case of resin composite restorations, HEMA and TEGDMA are available in microgram quantities via the salivary surface in the minutes and hours after clinical placement and via dentin and pulp in the hours and days after placement. Fortunately, moderate thickness of dentin protects pulp tissue against local toxicity. There are no data which suggest that systemic toxicity is a risk with any of these materials. There are some case reports of allergic responses to the monomers in patients, but the incidence of such responses appears at present to be much lower than that in dental personnel.

Oral insulin delivery using P(MAA-g-EG) hydrogels: effects of network morphology on insulin delivery characteristics

Hydrogels of poly(methacrylic acid-g-ethylene glycol) were prepared using different reaction water contents in order to vary the network mesh size, swelling behavior and insulin loading/release kinetics. Gels prepared with greater reaction solvent contents swelled to a greater degree and had a larger network mesh size. All of the hydrogels were able to incorporate insulin and protected it from release in acidic media. At higher pH (7.4), the release rates increased with reaction solvent content. Using a closed loop animal model, all of the insulin loaded formulations produced significant insulin absorption in the upper small intestine combined with hypoglycemic effects. In these studies, bioavailabilities ranged from 4.6% to 7.2% and were dependent on reaction solvent content.

The use of colloidal microgels as a (trans)dermal drug delivery system

A co-polymer of poly(N-isopropylacrylamide) (85%) co-butyl acrylate (10%) co-methacrylic acid (5%) (NIPAM/BA/MAA) (85/10/5) microgel was synthesised and investigated as a potential pH and temperature sensitive transdermal delivery device. Three compounds having different octanol/water partition coefficients and solubilities were incorporated into the microgel, namely: salicylamide (SA), methyl paraben (MP) and propyl paraben (PP). Physico-chemical characterisation of these microgel-drug complexes showed that microgels incorporating MP and SA have smaller volumes after changing environmental pH or temperature when compared with the co-polymer NIPAM/BA/MAA (85/10/5) alone. This reduction in volume could be attributed to the incorporation of the compounds into the microgel particles, having a shielding effect on the charged groups present within the network. Diffusion studies, across human skin, were performed at 305K in the range of pH 3-7 for saturated solutions of SA, MP and PP, and for microgel particles incorporating the three compounds. The transport rate for these microgels incorporating MP was reduced by 2/3-fold compared to the saturated solution, by one order of magnitude for PP, meanwhile the transport rate for these microgels incorporating SA is the same order of magnitude as that for the corresponding saturated solutions. Transdermal release studies of the saturated colloidal dispersions indicated that pH control of the drug release was marginal. The incorporation of compounds into the pH/temperature sensitive co-polymer NIPAM/BA/MAA (85/10/5) and the subsequent release depends on the octanol/water partition coefficient and solubility of the respective compound.

Effect of physicochemical modification on the biodistribution and tumor accumulation of HPMA copolymers

Copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) are prototypic and well-characterized polymeric drug carriers that are being broadly implemented in the delivery of anticancer therapeutics. To better predict the in vivo potential of the copolymers and to describe the biodistributional consequences of functionalization, 13 physicochemically different HPMA copolymers were synthesized, varying in molecular weight and in the nature and amount of functional groups introduced. Upon radiolabeling, the copolymers were injected i.v., and their circulation kinetics, tissue distribution and tumor accumulation were monitored in rats bearing subcutaneous Dunning AT1 tumors. It was found that increasing the average molecular weight of HPMA copolymers resulted in prolonged circulation times and in increased tumor concentrations. Conjugation of carboxyl and hydrazide groups, as well as introduction of spacer, drug and peptide moieties reduced the long-circulating properties of the copolymers and as a result, lower levels were found in tumors and in all organs other than kidney. Interestingly, however, in spite of the reduced (absolute) tumor concentrations, hardly any reduction in the relative levels localizing to tumors was found. Tumor-to-organ ratios were comparable to unmodified control for the majority of chemically modified copolymers, indicating that functionalization does not necessarily affect the tumor targeting ability of the copolymers and suggesting that HPMA copolymer-based drug delivery systems may prove to be attractive tools for more effectively treating various forms of advanced solid malignancy.

Preparation and characterization of intelligent core-shell nanoparticles based on poly(D,L-lactide)-g-poly(N-isopropyl acrylamide-co-methacrylic acid)

New thermo-responsive, pH-responsive, and biodegradable nanoparticles comprised of poly(D,L-lactide)-graft-poly(N-isopropyl acrylamide-co-methacrylic acid) (PLA-g-P(NIPAm-co-MAA)) were developed by grafting biodegradable poly(D,L-lactide) onto N-isopropyl acrylamide and methacrylic acid. A core-shell type nano-structure was formed with a hydrophilic outer shell and a hydrophobic inner core, which exhibited a phase transition temperature above 37 degrees C suitable for biomedical application. Upon heating above the phase transition temperature, PLA-g-P(NIPAm-co-MAA) nanoparticle showed a polarity increase of pyrene in either buffer solution or intra-hepato-carcinoma cells as determined by fluorescence measurement, indicating that the structure of nanoparticles caused leakages from outer shell copolymers aggregation and collapsed. The drug loading level of 5-fluorouracil (5-FU) encapsulated in the PLA-g-P(NIPAm-co-MAA) nanoparticles can be as high as 20%. The release of 5-FU from nanoparticles was strongly controlled by the pH in the aqueous solution. Based on these results, PLA-g-P(NIPAm-co-MAA) nanoparticles can be used as a drug carrier for intracellular delivery of anti-cancer drug.

Biodistribution and antitumour efficacy of long-circulating N-(2-hydroxypropyl)methacrylamide copolymer-doxorubicin conjugates in nude mice

The aim of this study was to evaluate the influence of the molecular weight (mol. wt) of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin (DOX) conjugates (P-DOX) on biodistribution and therapeutic efficacy in nu/nu mice bearing human ovarian carcinoma OVCAR-3 xenografts. Copolymerisation of HPMA, a polymerisable derivative of DOX (N-methacryloylglycylphenylalanylleucylglycyl doxorubicin) and a newly designed crosslinking agent, N(2),N(5)-bis(N-methacryloylglycylphenylalanyl-leucylglycyl)ornithine methyl ester monomers resulted in novel, high mol. wt, branched, water-soluble P-DOX containing lysosomally degradable oligopeptide sequences as crosslinks and side-chains terminated in DOX. Four conjugates with mol. wt of 22, 160, 895 and 1230 kDa were prepared. The results indicated that the half-life in blood and the elimination rate from the tumour were up to 28 times longer and 25 times slower, respectively, for P-DOX (mol. wt=1230 kDa) than for free DOX. Treatment with P-DOX (mol. wt > or = 160 kDa) inhibited tumour growth more efficiently than that of 22 kDa P-DOX or free DOX (P<0.02) at a 2.2 mg/kg DOX equivalent dose. In conclusion, the administration of long circulating P-DOX resulted in enhanced tumour accumulation with a concomitant increase in therapeutic efficacy.

The pharmacokinetics of polymer-bound adriamycin

Adriamycin (ADR) covalently bound to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers via biodegradable (Gly-Phe-Leu-Gly) oligopeptide sequences shows antitumour activity against model tumours in vivo. In this study we have examined the distribution of ADR bound to such HPMA copolymers following intravenous administration to mice (ADR concentration 5 mg/kg). An established fluorimetric HPLC method was used to measure levels of free ADR in plasma and tissue samples, and a new technique was developed to quantitate levels of polymer-bound anthracycline. The high initial levels of free ADR in plasma observed following administration of free drug were absent in the case of polymer-bound ADR, and the subsequently high levels of free ADR seen in other tissues were also abolished. In contrast, the circulating half-life of HPMA copolymer-ADR was approximately 15 times longer than that of the free drug. The initial peak level of free ADR in the heart was reduced 100-fold following administration of drug-conjugate. These alterations in pharmacokinetics may account for the decreased toxicity and improved efficacy reported previously.

Blends of enteric and GIT-insoluble polymers used for film coating: physicochemical characterization and drug release patterns

THE OBJECTIVES OF THIS STUDY WERE: (i). to use blends of gastrointestinal tract (GIT)-insoluble and enteric polymers (ethyl cellulose and Eudragit L) as coating materials for multiparticulate controlled release dosage forms; (ii). to investigate the effects of the polymer blend ratio and coating level on the resulting drug release patterns; and (iii). to explain the observed phenomena based on the physicochemical properties of the systems. Propranolol HCl-loaded pellets were coated in a fluidized bed coater with organic polymer solutions; thin, drug-containing and drug-free, polymeric films were prepared using a casting knife. In vitro drug release, water uptake and dry weight loss studies were performed in 0.1 M HCl and phosphate buffer pH 7.4, respectively. The apparent drug diffusion coefficients within the polymeric systems were determined using different experimental and theoretical techniques (side-by-side diffusion cells, in vitro drug release from thin films; exact and approximate solutions of Fick's second law of diffusion). A broad range of drug release patterns from coated pellets could be achieved by varying the GIT-insoluble:enteric polymer blend ratio. With increasing relative amounts of Eudragit L, the release rates in both media significantly increased. The increase at low pH could be attributed to an increase in water uptake, as observed with thin films. Interestingly, only partial Eudragit L leaching occurred in phosphate buffer pH 7.4 even at high enteric polymer contents, indicating that the GIT-insoluble polymer effectively hindered the dissolution of the entrapped Eudragit L. At high pH, both polymer leaching and polymer swelling contributed to the control of drug release. The determined apparent drug diffusion coefficients take the two effects adequately into account.

N-(2-hydroxypropyl)methacrylamide copolymers targeted to the hepatocyte galactose-receptor: pharmacokinetics in DBA2 mice

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymers containing doxorubicin (DOX) and galactosamine can be targeted to the hepatocyte galactose receptor for organ-specific chemotherapy of primary and metastatic liver cancer. Here we report the dose-dependent pharmacokinetics of this macromolecular conjugate. Following intravenous administration to mice most efficient liver targeting was seen at low dose (0.05 mg DOX kg-1), with receptor saturation observed using higher bolus doses. Repeated low dose bolus injections did not cause down-regulation of the galactose receptor and targeted drug delivery rates of greater than or equal to 2 micrograms DOX g-1 liver h-1 were achieved. DOX is released from such conjugates intracellularly via action of lysosomal proteinases. It was shown that isolated rat liver lysosomal enzymes (Tritosomes) can release unmodified DOX from the peptidyl side chain Gly-Phe-Leu-Gly at a rate greater than or equal to 3 micrograms DOX g-1 liver h-1 i.e. the hydrolytic capacity is greater than the observed rate of drug delivery to the liver lysosomes in vivo. Although most conjugate would be captured by normal hepatocytes following intravenous administration, it was shown that the human hepatoma cell line HepG2 retains the galactose receptor, accumulating and processing the conjugate efficiently. Potential dose limiting toxicities of such drug conjugates could include cardio- or hepatotoxicity. Administration of conjugate reduced the 15 min heart level of DOX approximately 100-fold compared with that observed for an equivalent dose of free drug. Preliminary experiments showed that plasma levels of alkaline phosphatase, alanine transaminase and asparate transaminase did not change following administration of HPMA copolymer-daunorubicin (DNR) (10 mg DNR kg-1) indicating no significant heptatoxicity.

Comparison of the anticancer effect of free and HPMA copolymer-bound adriamycin in human ovarian carcinoma cells

PURPOSE

To study peculiarities and the mechanism of the anticancer effect of free and HPMA copolymer-bound ADR in sensitive and resistant human ovarian carcinoma cells.

METHODS

Sensitive A2780 and ADR resistant A2780/AD cells were exposed to different doses of drugs during 12, 24, 36, 48, 60, and 72 hours. Cell viability, drug accumulation, apoptosis, cellular metabolism, lipid peroxidation, DNA content and gene expression were studied.

RESULTS

HPMA copolymer-bound ADR (P(GFLG)-ADR) possessed a comparable cytotoxicity to free ADR when comparison was based on intracellular concentrations. While free ADR up-regulated genes encoding ATP driven efflux pumps (MDR1, MRP), P(GFLG)-ADR overcame existing pumps and down regulated the MRP gene. Free ADR also activated cell metabolism and expression of genes responsible for detoxification and DNA repair. P(GFLG)-ADR down-regulated HSP-70, GST-pi, BUDP, Topo-IIalpha, beta, and TK-1 genes. Apoptosis, lipid peroxidation and DNA damage were significantly higher after exposure to P(GFLG)-ADR, as reflected by simultaneous activation of p53, c-fos in A2780 cells) or c-jun (A2780/AD) signaling pathways and inhibition of the bcl-2 gene. Differences between free ADR and P(GFLG)-ADR increased with the time of incubation and drug concentration.

CONCLUSIONS

P(GFLG)-ADR overcame drug efflux pumps, more significantly induced apoptosis and lipid peroxidation, inhibited DNA repair, replication, and biosynthesis when compared to free ADR.

Synthesis and in vivo pharmacokinetic evaluation of degradable shell cross-linked polymer nanoparticles with poly(carboxybetaine) versus poly(ethylene glycol) surface-grafted coatings

Nanoparticles with tunable pharmacokinetics are desirable for various biomedical applications. Poly(ethylene glycol) (PEG) is well-known to create "stealth" effects to stabilize and extend the blood circulation of nanoparticles. In this work, poly(carboxybetaine) (PCB), a new nonfouling polymer material, was incorporated as surface-grafted coatings, conjugated onto degradable shell cross-linked knedel-like nanoparticles (dSCKs) composed of poly(acrylic acid)-based shells and poly(lactic acid) cores, to compare the in vivo pharmacokinetics to their PEG-functionalized analogues. A series of five dSCKs was prepared from amphiphilic block copolymers, having different numbers and lengths of either PEG or PCB grafts, by supramolecular assembly in water followed by shell cross-linking, and then studied by a lactate assay to confirm their core hydrolytic degradabilities. Each dSCK was also conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid macrocyclic chelators and tyramine moieties to provide for (64)Cu and/or radiohalogen labeling. The high specific activity of (64)Cu radiolabeling ensured nanogram administration of dSCKs for in vivo evaluation of their pharmacokinetics. Biodistribution studies demonstrated comparable in vivo pharmacokinetic profiles of PCB-grafted dSCKs to their PEG-conjugated counterparts. These results indicated that PCB-functionalized dSCKs have great potential as a theranostic platform for translational research.

An Investigation into the In Vivo Performance Variability of pH Responsive Polymers for Ileo-Colonic Drug Delivery Using Gamma Scintigraphy in Humans

Gastrointestinal performance of tablets coated with pH responsive acrylic polymers (Eudragit) was investigated in human volunteers. Tablet cores were coated with Eudragit S dissolved in ethanol (organic), Eudragit S aqueous dispersion (aqueous), or Eudragit FS aqueous dispersion. Eight fasted volunteers received the tablets in a two-way crossover design-treatment 1: Eudragit S (organic) and Eudragit FS coated tablets; treatment 2: Eudragit S (aqueous) and Eudragit FS coated tablets. Eudragit FS coated tablets were included in both treatments to assess its intra-subject performance. Tablets were radiolabelled and followed by gamma scintigraphy; the disintegration times and positions were recorded. Tablets coated with Eudragit S (aqueous) disintegrated in all volunteers mainly in the proximal to mid small intestine. Eudragit S (organic) tablets failed to disintegrate in three out of eight volunteers, while disintegration was in the ileo-caecal junction and ascending colon in all others. Eudragit FS coated tablets disintegrated in 14 out of the 16 administrations. The Eudragit FS coated tablets that did disintegrate exhibited consistent intra- and inter-subject performance, with the site of disintegration focused on the ileo-caecal junction and ascending colon. These in vivo results correlate better with our published in vitro dissolution data in physiological bicarbonate buffers compared to phosphate buffers.

Limited exposure of the healthy distal colon to orally-dosed formulation is further exaggerated in active left-sided ulcerative colitis

BACKGROUND

Active distal ulcerative colitis is often resistant to topically acting oral formulations. We speculated that the left side of the colon is underexposed to orally-dosed topical agents in patients with active distal colitis.

METHODS

Twenty-two healthy volunteers (12 males, aged 22-47 years), and 10 patients (6 males, aged 33-73 years) with active left-sided ulcerative colitis ingested a Eudragit-coated gelatine capsule containing 111In-labelled amberlite resin on four successive days. Regional colonic distribution, transit times and percentage of daily dose resident were calculated from the average of four serial gamma camera images on the 4th day.

RESULTS

(mean [95% CI]). When compared to controls, patients with colitis had significantly faster total colon transit (24.3 h [9.5-39.1] vs. 51.7 h [41.1-62.3]) as well as faster proximal colon transit (18.7 h [9.1-28.3] vs. 36.7 [28.5-44.9]), and distal colon transit (3.1 h [-0.5 to 6.8] vs. 15.0 h [10.5-19.5]), respectively (all P < 0.01). Material was asymmetrically distributed in health (proximal colon 69% [63-76] vs. distal colon 31% [24-37]). This asymmetry was more extreme in colitis, with corresponding values of 91% [85-96] vs. 9% [4-15]. As a result colitics had less material in the left-sided colon (9% [4-15] vs. 31% [24-37]), P < 0. 001. Colitics had a significantly lower percentage of the daily dose resident within the left side of the colon compared to controls (13% [-2 to 28] vs. 63% [44-81]), P < 0.01.

CONCLUSIONS

Delayed release oral formulation is asymmetrically distributed within the colon in health. This asymmetry is exaggerated in active left-sided ulcerative colitis and, together with faster colonic transit, results in reduced exposure of the distal colon to orally-dosed topical agents.

PDEPT: polymer-directed enzyme prodrug therapy. I. HPMA copolymer-cathepsin B and PK1 as a model combination

Polymer-directed enzyme prodrug therapy (PDEPT) is a novel two-step antitumour approach using a combination of a polymeric prodrug and polymer-enzyme conjugate to generate cytotoxic drug selectively at the tumour site. In this study the polymeric prodrug N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-Gly-Phe-Leu-Gly-doxorubicin conjugate PK1 (currently under Phase II clinical evaluation) was selected as the model prodrug, and HPMA copolymer-cathepsin B as a model for the activating enzyme conjugate. Following polymer conjugation (yield of 30-35%) HPMA copolymer-cathepsin B retained approximately 20-25% enzymatic activity in vitro. To investigate pharmacokinetics in vivo,(125)I-labelled HPMA copolymer-cathepsin B was administered intravenously (i.v.) to B16F10 tumour-bearing mice. HPMA copolymer-cathespin B exhibited a longer plasma half-life (free cathepsin B t(1/2alpha)= 2.8 h; bound cathepsin B t(1/2alpha)= 3.2 h) and a 4.2-fold increase in tumour accumulation compared to the free enzyme. When PK1 (10 mg kg(-1)dox-equiv.) was injected i.v. into C57 mice bearing subcutaneously (s.c.) palpable B16F10 tumours followed after 5 h by HPMA copolymer-cathepsin B there was a rapid increase in the rate of dox release within the tumour (3.6-fold increase in the AUC compared to that seen for PK1 alone). When PK1 and the PDEPT combination were used to treat established B16F10 melanoma tumour (single dose; 10 mg kg(-1)dox-equiv.), the antitumour activity (T/C%) seen for the combination PDEPT was 168% compared to 152% seen for PK1 alone, and 144% for free dox. Also, the PDEPT combination showed activity against a COR-L23 xenograft whereas PK1 did not. PDEPT has certain advantages compared to ADEPT and GDEPT. The relatively short plasma residence time of the polymeric prodrug allows subsequent administration of polymer-enzyme without fear of prodrug activation in the circulation and polymer-enzyme conjugates have reduced immunogenicity. This study proves the concept of PDEPT and further optimisation is warranted.

A comparison between povidone-ethylcellulose and povidone-eudragit transdermal dexamethasone matrix patches based on in vitro skin permeation

The present study was designed to develop a suitable matrix type transdermal drug delivery system (TDDS) of dexamethasone using blends of two different polymeric combinations, povidone (PVP) and ethylcellulose (EC) and Eudragit with PVP. Physical studies including moisture content, moisture uptake, flatness to study the stability of the formulations and in vitro dissolution of the experimental formulations were performed to determine the amount of dexamethasone present in the patches were performed and scanning electron microscopy (SEM) photographs of the prepared TDDS were taken to see the drug distribution pattern. Drug-excipient interaction studies were carried out using Fourier transform infrared (FTIR) spectroscopic technique. In vitro skin permeation study was conducted in a modified Franz's diffusion cell. All the formulations were found to be suitable for formulating in terms of physicochemical characteristics and there was no significant interaction noticed between the drug and polymers used. In vitro dissolution studies showed that the drug distribution in the matrix was homogeneous and the SEM photographs further demonstrated this. The formulations of PVP:EC provided slower and more sustained release of drug than the PVP:Eudragit formulations during skin permeation studies and the formulation PVP:EC (1:5) was found to provide the slowest release of drug. Based on the above observations, it can be reasonably concluded that PVP-EC polymers are better suited than PVP-Eudragit polymers for the development of TDDS of dexamethasone.

Transmucosal delivery systems for calcitonin: a review

The commercial availability of peptides and proteins and their advantages as therapeutic agents have been the basis for tremendous efforts in designing delivery systems for such agents. The protection of these agents from biological fluids and physiological interactions is crucial for the treatment efficacy. One such agent is salmon calcitonin, a 32 amino-acid polypeptide hormone used in the treatment of bone diseases such as Paget's disease, hypercalcemia and osteoporosis. Researchers have studied different routes to deliver salmon calcitonin more effectively, including nasal, oral, vaginal and rectal delivery. These systems are designed to protect the polypeptide from the biological barriers that each delivery route imposes. Oil-based and polymer-based delivery systems are discussed.

Pharmacokinetic and biodistribution studies of a bone-targeting drug delivery system based on N-(2-hydroxypropyl)methacrylamide copolymers

Osteotropicity of novel bone-targeted HPMA copolymer conjugates has been demonstrated previously with bone histomorphometric analysis. The pharmacokinetics and biodistribution of this delivery system were investigated in the current study with healthy young BALB/c mice. The 125I-labeled bone-targeted and control (nontargeted) HPMA copolymers were administered intravenously to mice, and their distribution to different organs and tissues was followed using gamma counter and single photon emission computed tomography (SPECT). Both the invasive and noninvasive data further confirmed that the incorporation of D-aspartic acid octapeptide (D-Asp8) as bone-targeting moiety could favorably deposit the HPMA copolymers to the entire skeleton, especially to the high bone turnover sites. To evaluate the influence of molecular weight, three fractions (Mw of 24, 46, and 96 kDa) of HPMA copolymer-D-Asp8 conjugate were prepared and evaluated. Higher molecular weight of the conjugate enhanced the deposition to bone due to the prolonged half-life in circulation, but it weakened the bone selectivity. A higher content of bone-targeting moiety (D-Asp8) in the conjugate is desirable to achieve superior hard tissue selectivity. Further validation of the bone-targeting efficacy of the conjugates in animal models of osteoporosis and other skeletal diseases is needed in the future.

Effect of dentine on release of TEGDMA from resin composite in vitro

Triethylene glycol dimethacrylate (TEGDMA) is a component of some resin composites which contributes to their cytotoxicity. The presence of dentine between resin composite and test cells reduces the cytotoxicity in vitro. To determine why dentine has this protective effect, the diffusion of TEGDMA from a composite resin through dentine to the pulp space was compared with release directly into aqueous solution in vitro. Both release rate and total cumulative release of TEGDMA for the two groups, at times up to 100 days, were determined using reversed-phase HPLC. Release rate directly into water was highest in the minutes immediately after immersion and declined thereafter. However, in the tooth model, using an equivalent mass and surface area of composite resin, no TEGDMA was detectable in the pulp space until 43 min after restoration placement. The rate of diffusion through dentine from that time until day 1 was less than 1% of the highest (initial) direct release rate. The rate declined thereafter. It is relevant, however, that by day 3 the total cumulative release of TEGDMA through dentine was 60% of the direct release. Dentine therefore appears to exert its protective effect principally by retarding or 'damping' the initial high release of TEGDMA to a substantial degree.

Polymeric anticancer drugs with pH-controlled activation

The paper is dealing with the synthesis and properties of new, nontargeted or antibody-targeted pH-sensitive polymer-doxorubicin (DOX) conjugates designed as anticancer drugs facilitating site-specific therapy. These conjugates are stable and inactive during transport in the body but activate inside target cells as a result of pH changes outside and inside the cells. Cytotoxicity of the conjugates depends on the detailed structure of the polymer and of the spacer between the drug and polymer carrier. In both protective and therapeutic regimes of drug administration, the in vivo antitumor activity of the pH-sensitive conjugates containing DOX was significantly enhanced (T-cell lymphoma EL 4, C57BL/16 mice) in comparison with the free DOX or classic PK1, the PHPMA-DOX conjugate clinically tested at present.