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Nanoparticulate Drug Delivery: Perspectives on the Transition from Laboratory to Market
Автор: Vandana Patravale, Prajakta Dandekar и Ratnesh Jain
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Nanotechnology-based therapeutics, operating at scales of billionths of a metre, have great potential for future expansion in altering the scale and methods of drug delivery. The availability of these novel formulations to once-inaccessible areas of the body has greatly expanded the therapeutic window of existing drug molecules. Nanoparticulate drug delivery highlights and examines the transition of nanoparticulate drug delivery systems from the laboratory into a commercially viable sector. The first chapters of the book provide an overview of the use and characterization of nanoparticulate systems as drug carriers, including the assessment of their morphology, sterility and potential toxicity. In the latter part of the book, chapters cover nanotoxicology, regulatory aspect and clinical trials, ending with an overview of several case studies and a look towards future developments. Discusses the issues surrounding nanoparticulate products, based on personal experience of their formulation Provides an overview of new application areas, including RNA interference Outlines the pros and cons of nanoparticulate products, and discusses how these may influence their route into the commercial sector
Vandana Patravale
Vandana Patravale is a Professor of Pharmaceutics at the Department of Pharmaceutical Sciences and Technology, Institute of Chemical Technology, Mumbai, India. Her research group is actively involved in the design and development of colloidal drug delivery systems for various routes including oral, topical, transdermal, nasal and parenteral.
Соответствующие авторы
W. Roy Penney
Roy E. Sanders
Philip Ellenberger
Edward Whitticks
Gavin Towler
Swapan Basu
James R. Fair, PhD
Geoff B. Barker
Arthur Firstenberg
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Nanoparticulate Drug Delivery - Vandana Patravale
Nanoparticulate systems as drug carriers: the need
Development of nanoparticles for drug delivery has progressed by leaps and bounds over the last few decades, facilitating the possibility of an efficacious therapy for some fatal diseases. This development has stemmed from either the unsuitable physicochemical characteristics of the existing drug molecules, such as limited solubility and hence poor bioavailability, or the inadequacy of the conventional delivery systems to provide safe and efficient delivery. This chapter focuses on the precise need for the development of these novel nanoparticulate drug carriers and reasons for their popularity with the drug delivery scientists. The text also discusses the various strategies, including different formulation and targeting approaches, which have been adopted to overcome the challenges presented by the inherent properties of the drug molecules. Examples of nanoparticulate drug delivery systems which have already gained market approval have been cited in the discussion, wherever applicable.
nanoparticulate drug carriers
nanoemulsions
1.1 Introduction: nanoparticles for drug delivery
The last decade of drug delivery research has witnessed a boom in the development of the nano-drug delivery systems. The major drivers responsible for the initiation of this new revolution were the development of a plethora of varied nano-drug delivery systems, not only by the academic institutions but also by industrial organizations. This led to the availability of a huge database comprising several research papers and patents from all over world, describing these new dosage forms. Numerous funding agencies and industries actively promoted research into nanoparticulate drug delivery vehicles and huge investments were made to this end. All these diverse and concurrent efforts created an awareness about the immense potential of these new drug delivery systems, which were then looked upon as therapeutic regimens of the future.
There are many reasons behind the development and success of nanoparticulate drug delivery systems. A few years ago, the entire attention of pharmaceutical industry was focused on the novel developments in designing various dosage forms, primarily due to expiry of the existing patents, a surfeit of poorly soluble drug candidates and the problems of non-specificity from conventional dosage forms. Under these circumstances, the development of nanoparticulate drug delivery systems gained huge momentum due to a number of diverse factors listed in the following section of this chapter.
The pharmaceutical industries were poised to provide quality products to the patient, at the same time increasing or maintaining their profitability. However, this process demanded extensive scientific innovation and financial support. Development of new chemical entities and their transition from the laboratory to market required the company to expend as high as 800 million US dollars [1]. Apart from a huge investment, the development of the new drug was also an extensively time consuming process with very limited success rates.
Research progress in the drug discovery area resulted in the development of various poorly soluble drug candidates. The solubility limitations of these drug candidates, in turn, lead to poor bioavailability and lower therapeutic efficacy [2, 3]. In such situations, formulation of these therapeutic molecules into nanoparticulate delivery systems was observed to improve their bioavailability and hence elicit the desired therapeutic effects from these candidates. The nanoparticles also received a prominence due to other probable benefits like biodegradability, biocompatibility, high encapsulation characteristics and probability of surface functionalization [1–3].
Nanoparticles were found to exhibit several advantages for parenteral drug delivery; counter to the aggregation phenomenon commonly observed with microparticles, the smaller size of nanoparticles endowed them with better distribution profiles during systemic administration. Nanoparticles enabled an effective systemic circulation, thus leading to better therapeutic outcomes. Better systemic circulation was found to be specifically important for cancer therapies, where nanoparticles could infiltrate through the vasculature of tumor tissue and provide targeted therapeutic effects [4].
First pass metabolism is one of the key concerns for many commercial and upcoming drugs. This phenomenon accounts for their low bioavailability and reduced efficacy at the site of action. In this regard, nanoparticulate drug delivery vehicles were particularly advantageous because of their likelihood in being modulated for site specific delivery/ targeted delivery. Apart from their specificity, nanoparticles were also found to mitigate drug related side effects and dose related toxicities, resulting in enhanced bioavailability of the encapsulated agent and excellent patient compliance [1, 3, 5].
Owing to their small size, nanoparticles were found to effectively traverse many biological barriers. Of significant importance is their ability to permeate the blood brain barrier (BBB). Although brain administration is an effective route for the treatment of various brain diseases, it is severely limited due to the highly impermeable nature of the BBB. Because of their potential to cross this barrier, numerous publications have demonstrated the effectiveness of nanoparticles for targeting various central nervous system disorders [6]. Nanospectra Bioscience, Texas, USA, has recently initiated a clinical trial of nanoparticle based 'nanoshells' for the treatment of brain tumors [7].
The size of nanoparticles offers distinct advantages when compared with conventional dosage forms. The tunable size of these systems greatly influences the release profile of the encapsulated active component, so a formulator could thus control the drug release at the site of action [8, 9].
Nanoparticles were found to be highly versatile systems to encapsulate and delivery not only chemical drug moieties but also nuclic acid therapeutics (DNA, siRNA), and imaging and diagnostic agents, for site-specific delivery and detection. Various ligands can be attached to the surface of nanoparticles to guide them to specific locations within the body [9, 10].
Thus nanoparticulate drug carriers found applications in several diverse quarters of drug delivery research and, due to their tunable properties, they were foreseen as the future of the pharmaceutical and biotechnology industry.
1.2 Need: solubility, bioavailability, targeting and more
Drug transport through a biological barrier largely depends upon its solubility. Solubility exhibits an important influence on drug permeation and absorption. The solubility of drugs has been a concern for formulation scientists because of the difficulties in developing oral and parenteral delivery systems for poorly soluble drugs. Though the pharmaceutical sector is witnessing vast advances in drug discovery and its therapeutic horizon is expanding, it is the existing drug molecules and novel drug candidates that pose major solubility problems. Various reports indicate that approximately 40% of the drugs which are currently in the market have poor water solubility [11]. About one-third of the drug candidates in the pharmacopoeia exhibit the same solubility limitations. Low water solubility in turn hampers adequate absorption and hence leads to low therapeutic efficacy [12]. The solubility constraint of drugs and novel drug candidates is thus one of the major obstacles to the development of therapeutically effective drug delivery systems.
Nanoparticles made from natural/synthetic polymers, lipids, proteins and phospholipids have received greater attention due to higher stability and the opportunity for further surface modifications [13]. They can be tailored to achieve both controlled drug release and disease-specific localization, either by tuning the material characteristics or by altering the surface chemistry [14]. It has been established that nanocarriers can become concentrated preferentially in the tumor mass, sites of inflammation, and at sites of infection by virtue of the enhanced permeability and retention (EPR) effect of the vasculature. Once accumulated at the target site, hydrophobic biodegradable polymeric nanoparticles can act as a local drug depot, depending upon the make-up of the carrier, thus providing a reservoir for continuous supply of encapsulated therapeutic compound at the disease site, such as, a solid tumor. These systems, in general, can be used to provide targeted (cellular/tissue) delivery of drugs, to improve oral bioavailability, to sustain drug/gene effects in the target tissue, to solubilize drugs for intravascular delivery, or to improve the stability of therapeutic agents against enzymatic degradation (nucleases and proteases), this being especially relevant for protein, peptide, and nucleotide based agents [13, 15, 16]. Thus, the advantages of using nanoparticles for drug delivery result from two main basic properties: their small size and the use of biodegradable materials.
Many studies have demonstrated that nanoparticles of sub-micron size have a number of advantages over conventional dosage forms as drug delivery carriers [17]. A further advantage over conventional drug delivery systems is their better suitability for intravenous (i.v.) delivery. The smallest capillaries in the body are 5–6 μm in diameter. Therefore the size of particles being distributed into the bloodstream must be significantly smaller than 5 μm, without forming aggregates, to ensure that the particles do not lead to an embolism. Additionally, some types of cells permit the uptake of only sub-micron particles and not their larger counterparts. Generally nanoparticles have relatively higher intracellular uptake compared to microparticles and are available to a much wider range of biological targets due to their small size and relative mobility. Desai et al. found that 100 nm nanoparticles had a 2.5 fold greater uptake than 1 μm microparticles, and 6 fold greater uptake than 10 μm microparticles in a CaCo– 2 cell line [16]. Secondly, the use of biodegradable materials for nanoparticle preparation allows sustained drug release within the target site over a period of days or even weeks.
With regards to the material of formulation, biodegradable nanoparticles formulated from polymers and lipids have been developed for intracellular sustained drug delivery, especially for drugs with an intracellular target [13, 16]. Rapid escape of these nanoparticles from the endo-lysosomal compartment to the cytoplasmic compartment has been demonstrated [13, 17]. Additionally, they were demonstrated to effectively sustain the intracellular drug levels, thus allowing a more efficient interaction with the cytoplasmic receptors. Thus, nanoparticles could serve as effective delivery vehicles for drugs with cytoplasmic targets.
To summarize, nanoparticles have proven advantages over the conventional dosage forms. They offer a reliable alternative to the pharmaceutical industry to improve the therapeutic effects of existing drugs, elicit better effect from new chemical entities and to deliver sensitive molecules like proteins, peptides, DNA and RNA.
1.3 Specific nanoparticulate strategies for overcoming solubility and bioavailability limitations
1.3.1 Nanoemulsions
Nanoemulsions are optically isotropic and thermodynamically stable systems of two immiscible liquids – typically water, oil and surfactant(s) – in which one liquid is dispersed as droplets in another liquid. Emulsions with nanoscopic droplet sizes (typically in the range of 20–200 nm) are often referred to as nanoemulsions [18]. Nanoemulsions offer enhanced solubilization capacity for poorly soluble drugs, increased drug loading, and in turn lead to a higher bioavailability of the formulated therapeutic moiety. Various GRAS (generally regarded as safe) approved, saturated and unsaturated fatty acids and nonionic surfactants are commonly used for formulating the nanoemulsions. The formulation of nanoemulsions can either involve appropriate energy inputs (ultrasonication, high pressure homogenization, microfluidization) or may be a spontaneous process. There are a few commercial products like Estrasorb® and Flexogan® which are based on nanoemulsion technology [19, 20]. Estrasorb® is estradiol topical emulsion developed by Novavax and is recommended for the reduction of vasomotor symptoms in menopausal women. Estrasorb® is composed of soyabean oil, water, polysorbate 80 and water and is based on micellar nanoparticle technology. This technology proves that poorly water soluble molecules like estradiol can be successfully formulated and commercialized using nanoparticulate delivery vehicles [20, 21].
Yet another example of a nanoemulsion based product is that of Flexogan® developed by AlphaRx, Canada, which is a pain relief cream based on colloidal dispersion of nanoparticles. The oil droplets contain natural pain medicaments like menthol and camphor and as nanoparticles permeating faster through the skin, thereby providing a rapid relief. Once again in this case the nanoparticulate delivery is responsible for a higher bioavailability and quicker onset of action of the encapsulated actives
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