R. Karl Malcolm's research while affiliated with Queen's University Belfast and other places

Publications (103)

Article
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Capsular contracture is a common complication associated with breast implants following reconstructive or aesthetic surgery in which a tight or constricting scar tissue capsule forms around the implant, often distorting the breast shape and resulting in chronic pain. Capsulectomy (involving full removal of the capsule surrounding the implant) and c...
Article
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Steroid-releasing vaginal rings are available for contraception and estrogen replacement therapy, and a new antiretroviral-releasing ring was recently approved for HIV prevention. Marketed rings are white or transparent in appearance, non-scented, and supplied as one-size-fits-all devices with diameters ranging from 54 to 56 mm. In this study, drug...
Article
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Bacterial vaginosis (BV) is a common dysbiosis of the human vagina in which commensal vaginal lactobacilli are displaced by mixed pathogenic bacterial populations. Current treatments by antibiotics result in short- term cure but often lead to recurrence. Lactobacilli are being actively developed as a probiotic treatment option for BV, given their a...
Article
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We have previously reported a multipurpose silicone elastomer vaginal ring providing sustained release of dapivirine (an antiretroviral) and levonorgestrel (a progestin) for HIV prevention and hormonal contraception. During initial development, issues arose due to reaction between the ethynyl group in the levonorgestrel molecule and the hydride-fun...
Article
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A dapivirine-releasing silicone elastomer vaginal ring for reducing women's risk of HIV acquisition has recently been approved. A next-generation multipurpose vaginal ring releasing dapivirine and levonorgestrel is currently in development, offering hormonal contraception and HIV prevention from a single device. Previously, we reported challenges w...
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Previously reported in vitro release test methods for drug-releasing vaginal rings containing poorly water-soluble drugs have described use of water-alcohol systems or surfactant solutions in efforts to maintain sink conditions. Here, as part of efforts to more closely match in vitro and in vivo release for the 25 mg dapivirine matrix-type silicone...
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The diversity and dynamics of the microbial species populating the human vagina are increasingly understood to play a pivotal role in vaginal health. However, our knowledge about the potential interactions between the vaginal microbiota and vaginally administered drug delivery systems is still rather limited. Several drug-releasing vaginal ring pro...
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Vaginal rings releasing antiretrovirals – either alone or in combination with contraceptive progestins – are being developed for prevention of human immunodeficiency virus (HIV) transmission via vaginal sex. Following Phase I trials, significant discoloration was observed on the surface of investigational silicone elastomer antiretroviral-contracep...
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Introduction There is considerable interest in vaginal ring technology for sustained/controlled release of pharmaceutical drugs to the human vagina. Seven drug-releasing vaginal ring products have reached market and have many other experimental devices are in preclinical/clinical development. Although most women who have use vaginal rings are satis...
Article
Here we report the first use of an additive manufacturing (AM) technique based on high pressure material jetting of molten thermoplastic for the fabrication of dapivirine (DPV) loaded vaginal rings (VRs). The VRs are compared to those produced conventionally using injection molding (IM). VRs (outer diameter 54.0 mm, cross-sectional diameter 4.0 mm)...
Article
Drug-releasing vaginal rings are torus-shaped devices, generally fabricated from thermoplastics or silicone elastomers, used to administer pharmaceutical drugs to the human vagina for periods typically ranging from three weeks to twelve months. One of the most important product performance tests for vaginal rings is the in vitro release test. Altho...
Article
With a dapivirine-releasing vaginal ring having successfully completed late-stage clinical testing for HIV prevention and currently undergoing regulatory review, there is now growing interest in next-generation multipurpose prevention technologies that seek to combine antiretroviral and contraceptive drugs within a single product. Here, we focus on...
Article
The past fifteen years have witnessed a resurgence of interest in vaginal ring technologies for drug delivery applications, mostly driven by the impetus for development of vaginally-administered antiretroviral microbicides to help reduce the high acquisition rates for human immunodeficiency virus (HIV) among Sub-Saharan African women. Currently, th...
Article
Objectives: The primary aim was to investigate post-use ring weight as a potential measure of cumulative adherence to a progesterone-releasing vaginal ring. Study design: We weighed and quantified residual progesterone in 115 vaginal rings following 90-day use by participants in an acceptability trial conducted in Nigeria, Senegal and Kenya. The...
Article
In two recent Phase III clinical trials, use of a 25 mg dapivirine vaginal ring significantly reduced HIV acquisition rates. Post hoc analysis from one of the trials indicated higher rates of protection among women over the age of 21 years when compared to younger women, most likely due to reduced adherence in the latter group. There is currently n...
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Antiretroviral-releasing vaginal rings are at the forefront of ongoing efforts to develop microbicide-based strategies for prevention of heterosexual transmission of the human immunodeficiency virus (HIV). However, traditional ring designs are generally only useful for vaginal administration of relatively potent, lipophilic, and small molecular wei...
Article
Vaginal rings (VRs) are currently marketed for contraceptive or hormone regulation purposes, and investigationally, have been widely reported for delivery of antiretrovirals to reduce HIV transmission. To date, there is no national or international standard for the mechanical testing and minimum performance characteristics of any VR based products....
Article
This work investigates the impact of vaginal ring size and drug loading on the in vitro release, safety, ease of fit, and pharmacokinetics in cynomolgus macaques of matrix-type silicone elastomer vaginal rings containing a combination of the non-nucleoside reverse transcriptase inhibitor dapivirine and the protease inhibitor darunavir. Drug-free an...
Article
Steroid molecules have a long history of incorporation into silicone elastomer materials for controlled release drug delivery applications. Previously, based on in vitro release testing and drug content analysis, we demonstrated indirectly that the contraceptive progestin levonorgestrel (LNG) chemically and irreversibly binds to addition cure silic...
Article
Intravaginal rings (VRs) have been widely reported for administration of pharmaceutical drugs - most notably estrogens, progestogens and antiretrovirals - to the vagina for clinical benefit. Here, for the first time, we describe the design, manufacture and preclinical testing of VRs for sustained/controlled release of the cervical ripening agents i...
Article
5P12-RANTES, a chemokine analogue that potently blocks the HIV CCR5 co-receptor, is being developed as both a vaginal and rectal microbicide for prevention of sexual transmission of HIV. Here, we report the first pharmacokinetic data for 5P12-RANTES, following single dose vaginal gel administration in sheep. Aqueous gel formulations containing low...
Article
A silicone elastomer vaginal ring providing sustained release over 28 days of the antiretroviral microbicide dapivirine has recently completed Phase III clinical testing and showed moderate protection against HIV acquisition. In support of the product licensure program, we report the impact of dapivirine packing polymorphism on the thermal and solu...
Data
Excised sheep vagina at necropsy. A vaginal ring antigen-release device in situ within a vagina removed from a culled sheep. No inflammation or infection is apparent on the vaginal vault wall. Note that the lyophilized rod that originally contained the vaccine formulation is no longer present in the visible ring cavity.
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The generation of effective levels of antigen-specific immunity at the mucosal sites of pathogen entry is a key goal for vaccinologists. We explored topical vaginal application as an approach to initiate local antigen-specific immunity, enhance previously existing systemic immunity or re-target responses to the mucosae. To deliver a protein vaccine...
Article
A matrix-type silicone elastomer vaginal ring providing 28-day continuous release of dapivirine (DPV) - a lead candidate human immunodeficiency virus type 1 (HIV-1) microbicide compound - has recently demonstrated moderate levels of protection in two Phase III clinical studies. Here, next-generation matrix and reservoir-type silicone elastomer vagi...
Article
Despite a long history of incorporating steroids into silicone elastomers for drug delivery applications, little is presently known about the propensity for irreversible drug binding in these systems. In this study, the ability of the contraceptive progestin levonorgestrel to bind chemically with hydrosilane groups in addition-cure silicone elastom...
Article
Vaginal rings (VRs) are flexible, torus-shaped, polymeric devices designed to sustain delivery of pharmaceutical drugs to the vagina for clinical benefit. Following first report in a 1970 patent application, several steroid-releasing VR products have since been marketed for use in hormone replacement therapy and contraception. Since 2002, there has...
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Administration of biomacromolecular drugs in effective quantities from conventional vaginal rings is hampered by poor drug permeability in the polymers from which rings are commonly constructed. Here, we report the formulation development and testing of rod insert rings for sustained release of the candidate antiretroviral peptides T-1249 and JNJ54...
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Background: Product adherence is a pivotal issue in the development of effective vaginal microbicides to reduce sexual transmission of HIV. To date, the six Phase III studies of vaginal gel products have relied primarily on self-reporting of adherence. Accurate and reliable methods for monitoring user adherence to microbicide-releasing vaginal rin...
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This study describes the preclinical development of a matrix-type silicone elastomer vaginal ring device designed to provide controlled release of UC781, a non-nucleoside reverse transcriptase inhibitor. Testing of both human- and macaque-sized rings in a sink condition in vitro release model demonstrated continuous UC781 release in quantities cons...
Chapter
The overwhelming majority of vaccine antigens are biological macromolecules, such as proteins and polysaccharides, typically with a molecular weight greater than 10,000. As such, they need to be delivered to the body in the correct conformation in order to elicit the desired immune response and to effectively target the immune cells. Currently, mos...
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Objectives: Combination microbicide vaginal rings may be more effective than single microbicide rings at reducing/preventing sexual transmission of HIV. Here, we report the pre-clinical development and macaque pharmacokinetics of matrix-type silicone elastomer vaginal rings containing dapivirine and darunavir. Methods: Macaque rings containing 2...
Article
We previously reported nonaqueous silicone elastomer gels (SEGs) for sustained vaginal administration of the CCR5-targeted entry inhibitor maraviroc (MVC). Here, we describe chemically modified SEGs (h-SEGs) in which the hydrophobic cyclomethicone component was partially replaced with relatively hydrophilic silanol-terminated polydimethylsiloxanes...
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This study measured and compared the pharmacokinetics of CMPD167, a small molecule antiretroviral CCR5 inhibitor with potential as an HIV microbicide, following vaginal, rectal and oral administration in rhesus macaques. A vaginal hydroxyethylcellulose (HEC) gel, a rectal HEC gel, a silicone elastomer matrix-type vaginal ring and an oral solution,...
Article
J Antimicrob Chemother 2013; 68: 394–403 This paper is now available as Open Access. The copyright line should read as follows: This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc/3.0/), which permits non-commercial reuse, distribution, and reproduction...
Article
To formulate therapeutic proteins into polymeric devices the protein is typically in the solid state, which can be achieved by the process of freeze‐drying. However, freeze‐drying not only risks denaturing the protein but it can adversely affect the cure characteristics of protein‐loaded silicone elastomers. This study demonstrates that a variation...
Article
Vaginal rings are currently being developed for the long-term (at least 30 days) continuous delivery of microbicides against human immunodeficiency virus (HIV). Research to date has mostly focused on devices containing a single antiretroviral compound, exemplified by the 25 mg dapivirine ring currently being evaluated in a Phase III clinical study....
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UC781 is potent, hydrophobic, non-nucleotide reverse transcriptase inhibitor (NNRTI) against the human immunodeficiency virus (HIV). UC781 is currently being investigated for use as a potential HIV microbicide. A study in rhesus macaques demonstrated that a 100-mg UC781-loaded silicone elastomer vaginal ring released limited amounts of UC781 into t...
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Following the successful development of long-acting steroid-releasing vaginal ring devices for the treatment of menopausal symptoms and contraception, there is now considerable interest in applying similar devices to the controlled release of microbicides against HIV. In this review article, the vaginal ring concept is first considered within the w...
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Objectives: To investigate the pharmacokinetics (PK) of maraviroc, a CCR5-targeted HIV-1 entry inhibitor, in rhesus macaques following vaginal administration of various maraviroc-loaded aqueous hydroxyethylcellulose (HEC) gels, and to correlate the PK data with efficacy in a single high-dose vaginal SHIV-162P3 challenge model. Methods: Maraviroc...
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Objectives: The non-nucleoside reverse transcriptase inhibitor MC1220 has potent in vitro activity against HIV type 1 (HIV-1). A liposome gel formulation of MC1220 has previously been reported to partially protect rhesus macaques against vaginal challenge with a simian HIV (SHIV). Here, we describe the pre-clinical development of an MC1220-releasi...
Article
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Dissolving polymeric microneedle arrays formulated to contain recombinant CN54 HIVgp140 and the TLR4 agonist adjuvant MPLA were assessed for their ability to elicit antigen-specific immunity. Using this novel microneedle system we successfully primed antigen-specific responses that were further boosted by an intranasal mucosal inoculation to elicit...
Article
Vaginal rings are currently being investigated for delivery of HIV microbicides. However, vaginal rings are currently manufactured form hydrophobic polymers such as silicone elastomer and polyethylene vinyl acetate (PEVA), which do not permit release of hydrophilic microbicides such as the nucleotide reverse transcriptase inhibitor tenofovir. Biode...
Article
Silicone elastomer systems have previously been shown to offer potential for the sustained release of protein therapeutics. However, the general requirement for the incorporation of large amounts of release enhancing solid excipients to achieve therapeutically effective release rates from these otherwise hydrophobic polymer systems can detrimentall...
Article
A major goal in vaccine development is elimination of the 'cold chain', the transport and storage system for maintenance and distribution of the vaccine product. This is particularly pertinent to liquid formulation of vaccines. We have previously described the rod-insert vaginal ring (RiR) device, comprising an elastomeric body into which are inser...
Article
We will describe in vitro and rhesus macaque studies aimed at developing a coitally-independent delivery system(s) for vaginal microbicides. In this work, we have focused on the small molecule CCR5 inhibitors CMPD167 and Maraviroc. We have formulated these compounds in vaginal rings that can remain in situ for up to a month while gradually releasin...
Article
Mucosally-administered vaccine strategies are widely investigated as a promising means of preventing HIV infection. This study describes the development of liposomal gel formulations, and novel lyophilised variants, comprising HIV-1 envelope glycoprotein, CN54gp140, encapsulated within neutral, positively charged or negatively charged liposomes. Th...
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Antiretroviral entry inhibitors are now being considered as vaginally administered microbicide candidates for the prevention of the sexual transmission of human immunodeficiency virus. Previous studies testing the entry inhibitors maraviroc and CMPD167 in aqueous gel formulations showed efficacy in the macaque challenge model, although protection w...
Article
Aqueous semi-solid polymeric gels, such as those based on hydroxyethylcellulose (HEC) and polyacrylic acid (e.g. Carbopol®), have a long history of use in vaginal drug delivery. However, despite their ubiquity, they often provide sub-optimal clinical performance, due to poor mucosal retention and limited solubility for poorly water-soluble actives....
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Vaccine-mediated prevention of primary HIV-1 infection at the heterosexual mucosal portal of entry may be facilitated by highly optimised formulations or drug delivery devices for intravaginal (i.vag) immunization. Previously we described hydroxyethylcellulose (HEC)-based rheologically structured gel vehicles (RSVs) for vaginal immunization of an H...
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UC781 is a potent and poorly water-soluble nonnucleoside reverse transcriptase inhibitor being investigated as a potential microbicide for preventing sexual transmission of HIV-1. This study was designed to evaluate the in vivo release and pharmacokinetics of UC781 delivered from matrix-type intravaginal ring segments in rabbits. Three polymer matr...
Article
Over half of all HIV-infected adults are women and heterosexual intercourse is a significant mode of viral transmission. This review examines the potential for using polymeric vaginal ring systems to provide controlled delivery of HIV microbicides in order to prevent heterosexual transmission of the virus. Continuous delivery of microbicides has th...
Article
Vaginal ring devices capable of providing sustained/controlled release of incorporated actives are already marketed for steroidal contraception and estrogen replacement therapy. In recent years, there has been considerable interest in developing similar ring devices for the administration of microbicidal compounds to prevent vaginal HIV transmissio...
Article
The present investigation dealswith development and characterization of the liposomes-based freeze-dried rods for the vaginal delivery of gp140 antigen in mice. Positively charged, negatively charged and neutral liposomes were prepared and characterized for various parameters e.g. morphology, size, polydispersity index, zeta potential and antigen e...
Article
A new vaginal ring technology, the insert vaginal ring (InVR), is presented. The InVR overcomes the current shortfall of conventional vaginal rings (VRs) that are generally ineffectual for the delivery of hydrophilic and/or macromolecular actives, including peptides, proteins and antibodies, due to their poor permeation characteristics in the hydro...
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Silicone elastomer systems have been shown to offer potential for the fabrication of medical devices and sustained release drug delivery devices comprising low molecular weight drugs and protein therapeutics. For drug delivery systems in particular, there is often no clear rationale for selection of the silicone elastomer grade, particularly in res...
Article
Dapivirine mucoadhesive gels and freeze-dried tablets were prepared using a 3x3x2 factorial design. An artificial neural network (ANN) with multi-layer perception was used to investigate the effect of hydroxypropyl-methylcellulose (HPMC): polyvinylpyrrolidone (PVP) ratio (X1), mucoadhesive concentration (X2) and delivery system (gel or freeze-dried...
Article
Bovine serum albumin (BSA) is a commonly used model protein in the development of pharmaceutical formulations. In order to assay its release from various dosage forms, either the bicinchoninic acid (BCA) assay or a more specific size-exclusion high performance liquid chromatography (SE-HPLC) method are commonly employed. However, these can give err...
Article
Microbial adhesion to silicone elastomer biomaterials is a major problem often resulting in infection and medical device failure. Several strategies have been employed to modulate eukaryotic cell adhesion and to hamper bacterial adherence to polymeric biomaterials. Chemical modification of the surface by grafting of polyethylene glycol (PEG) chains...