Cell-based apoptosis assays in oncology drug discovery

Importance of the field: Screening compounds with a cell-based phenotypic approach complements target-based discovery programs because of the opportunity to investigate targets in the context of the cellular milieu and to discover novel targets.

Areas covered in this review: Utilizing a cell-based apoptotic phenotype screen for discovery and optimization of apoptosis inducers and affirming activity as potential anticancer agents in vivo with xenograft models. Subsequently, chemical genetic tools are utilized to identify and validate previously unrecognized cancer targets. Case studies showing the various multidisciplinary approaches utilized for several years are reviewed.

What the reader will gain: The interactive nature of the drug and target discovery processes, and insights that come from integration of cellular biology, medicinal chemistry and animal research.

Take home message: Phenotype proapoptotic screen followed by chemical genetics is useful for anticancer drug research, for the discovery of potential drugs and identification of druggable targets.     

Cell-based apoptosis assays in oncology drug discovery

Importance of the field: Screening compounds with a cell-based phenotypic approach complements target-based discovery programs because of the opportunity to investigate targets in the context of the cellular milieu and to discover novel targets. Areas covered in this review: Utilizing a cell-based apoptotic phenotype screen for discovery and optimization of apoptosis inducers and affirming activity as potential anticancer agents in vivo with xenograft models. Subsequently, chemical genetic tools are utilized to identify and validate previously unrecognized cancer targets. Case studies showing the various multidisciplinary approaches utilized for several years are reviewed. What the reader will gain: The interactive nature of the drug and target discovery processes, and insights that come from integration of cellular biology, medicinal chemistry and animal research. Take home message: Phenotype proapoptotic screen followed by chemical genetics is useful for anticancer drug research, for the discovery of potential drugs and identification of druggable targets.     

Cell-based in vitro models for predicting drug permeability

INTRODUCTION: In vitro cell models have been used to predict drug permeation in early stages of drug development, since they represent an easy and reproducible method, allowing the tracking of drug absorption rate and mechanism, with an advantageous cost-benefit ratio. Such cell-based models are mainly composed of immortalized cells with an intrinsic ability to grow in a monolayer when seeded in permeable supports, maintaining their physiologic characteristics regarding epithelium cell physiology and functionality. AREAS COVERED: This review summarizes the most important intestinal, pulmonary, nasal, vaginal, rectal, ocular and skin cell-based in vitro models for predicting the permeability of drugs. Moreover, the similitude between in vitro cell models and in vivo conditions are discussed, providing evidence that each model may provisionally resemble different drug absorption route. EXPERT OPINION: Despite the widespread use of in vitro cell models for drug permeability and absorption evaluation purposes, a detailed study on the properties of these models and their in vitro-in vivo correlation compared with human data are required to further use in order to consider a future drug discovery optimization and clinical development.     

Site-specific drug delivery systems. III. Nasal drug delivery

The nasal cavity has a large surface and a rich blood supplied mucosa. Drugs absorbed by blood vessels pass directly into the systemic circulation, thereby avoiding first-pass metabolism. Numbers of factors limit the intranasal absorption of drugs, especially peptide and protein drugs. These factors are the epithelial and mucus barrier, the rapid mucociliar clearance and the enzymatic activity. Increasing the residence time of the drug formulation in the nasal cavity and a period of contact with nasal mucosa, may improve drug absorption. Approaches to increase the residence time of drug formulations in the nasal cavity usually involve the use of microspheres, liposomes and bioadhesive gels.     

胞内酶敏感肿瘤靶向递药体系的合成及应用

目的利用对乳腺癌肿瘤细胞MDA-MB-435内特有酶豆蛋白酶(legumain)敏感的多肽(AANL)连接阿霉素(DOX)构建具有胞内特异性释药功能的纳米递药系统,并对AANL在含有legumain环境下的断裂效率进行研究。方法将DOX用AANL修饰得到AANL-DOX(AD),再将AD连接至4-arm PEG上,最后将细胞穿膜肽(TAT)连接至4-arm PEG-AD上,制备出TAT-PEG-AD并自组装形成纳米粒(TPAD)。核磁表征TAT-PEG-AANL-DOX;粒度分析仪和透射电镜测定纳米粒的粒径及外观形貌;模拟体内、肿瘤微环境和胞内环境通过动态透析法研究legumain对AANL的断裂效率并模拟DOX的药物控释效率;细胞毒性研究TPAD对MDA-MB-435细胞的毒性作用。结果核磁共振氢谱证实TAT-PEG-AANL-DOX合成成功;测定TPAD的粒径为126.3 nm;透射电镜(TEM)观察纳米粒结构圆整,粒径为80 nm;24 h的累积释药量为82.2%;体外细胞毒性研究表明,TPAD对MDA-MB-435细胞有较好的杀伤作用,其效果接近游离DOX的细胞毒性。结论利用legumain敏感多肽连接DOX制备具有胞内特异性释药功能的纳米粒,能够有效实现肿瘤细胞内晚期内涵体和溶酶体精准释药,提高抗肿瘤药物的生物利用度,值得进一步研究。     

Pulsed drug delivery

Modern drug delivery aims to develop drug delivery systems that are able to meet specific therapeutic requirements. Whereas sustained drug release aims to maintain a constant drug level within the body, pulsed drug delivery intends to release the drug rapidly within a short period of time, as a result of a biological or external trigger, after a specific lag time. This editorial highlights some of the recent advances in new concepts for pulsed drug delivery and proposes some future strategies.     

Pulsed drug delivery

Modern drug delivery aims to develop drug delivery systems that are able to meet specific therapeutic requirements. Whereas sustained drug release aims to maintain a constant drug level within the body, pulsed drug delivery intends to release the drug rapidly within a short period of time, as a result of a biological or external trigger, after a specific lag time. This editorial highlights some of the recent advances in new concepts for pulsed drug delivery and proposes some future strategies.     

药物的鼻腔黏膜吸收

鼻腔给药具有诸多优点，如能够避免肝脏的首过效应和胃肠道的降解，提高化学药物和肽类药物的生物利用度；增加药物向脑内递释，提高脑部疾病的治疗效果；具有特有的免疫性质等。介绍药物鼻腔黏膜吸收的特点和影响因素，综述鼻腔给药制剂的研究方法和研制情况，旨为该领域研究提供参考。     

Cell-mediated drug delivery

INTRODUCTION: Drug targeting to sites of tissue injury, tumor or infection with limited toxicity is the goal for successful pharmaceutics. Immunocytes (including mononuclear phagocytes (dendritic cells, monocytes and macrophages), neutrophils and lymphocytes) are highly mobile; they can migrate across impermeable barriers and release their drug cargo at sites of infection or tissue injury. Thus, immune cells can be exploited as Trojan horses for drug delivery. AREAS COVERED: This paper reviews how immunocytes laden with drugs can cross the blood-brain or blood-tumor barriers to facilitate treatments for infectious diseases, injury, cancer, or inflammatory diseases. The promises and perils of cell-mediated drug delivery are reviewed, with examples of how immunocytes can be harnessed to improve therapeutic end points. EXPERT OPINION: Using cells as delivery vehicles enables targeted drug transport and prolonged circulation times, along with reductions in cell and tissue toxicities. Such systems for drug carriage and targeted release represent a new disease-combating strategy being applied to a spectrum of human disorders. The design of nanocarriers for cell-mediated drug delivery may differ from those used for conventional drug delivery systems; nevertheless, engaging different defense mechanisms in drug delivery may open new perspectives for the active delivery of drugs.     

Erythrocyte-based drug delivery

The use of a physiological carrier to deliver therapeutics throughout the body to both improve their efficacy while minimising inevitable adverse side effects, is an extremely fascinating perspective. The behaviour of erythrocytes as a delivery system for several classes of molecules (i.e., proteins, including enzymes and peptides, therapeutic agents in the form of nucleotide analogues, glucocorticoid analogues) has been studied extensively as they possess several properties, which make them unique and useful carriers. Furthermore, the possibility of using carrier erythrocytes for selective drug targeting to differentiated macrophages increases the opportunities to treat intracellular pathogens and to develop new drugs. Finally, the availability of an apparatus that permits the encapsulation of drugs into autologous erythrocytes has made this technology available in many clinical settings and competitive with other drug delivery systems.     

Ocular drug delivery

Drug delivery to the eye is hampered by anatomical factors, including the corneal epithelium, the blood–aqueous barrier and the blood–retinal barrier. This review aims to outline the major routes of ocular drug delivery, including systemic, topical, periocular and intravitreal. The pharmacokinetics, the disadvantages and the clinical relevance of these drug delivery routes have been emphasised. Recent advances in surgical techniques, therapeutic approaches and material sciences have produced exciting new therapies for ocular diseases. The role of ophthalmic drug formulation in targeting the desired ocular tissue and enhancing drug delivery by the chosen route whilst minimising side effects is also discussed.     

Buccal drug delivery

Buccal formulations have been developed to allow prolonged localised therapy and enhanced systemic delivery. The buccal mucosa, however, while avoiding first-pass effects, is a formidable barrier to drug absorption, especially for biopharmaceutical products (proteins and oligonucleotides) arising from the recent advances in genomics and proteomics. The buccal route is typically used for extended drug delivery, so formulations that can be attached to the buccal mucosa are favoured. The bioadhesive polymers used in buccal drug delivery to retain a formulation are typically hydrophilic macro-molecules containing numerous hydrogen bonding groups. Newer second-generation bioadhesives have been developed and these include modified or new polymers that allow enhanced adhesion and/or drug delivery, in addition to site-specific ligands such as lectins. Over the last 20 years a wide range of formulations has been developed for buccal drug delivery (tablet, patch, liquids and semisolids) but comparatively few have found their way onto the market. Currently, this route is restricted to the delivery of a limited number of small lipophilic molecules that readily cross the buccal mucosa. However, this route could become a significant means for the delivery of a range of active agents in the coming years, if the barriers to buccal drug delivery are overcome. In particular, patient acceptability and the successful systemic delivery of large molecules (proteins, oligonucleotides and polysaccharides) via this route remains both a significant opportunity and challenge, and new/improved technologies may be required to address these.     

Iontophoretic drug delivery

The composition and architecture of the stratum corneum render it a formidable barrier to the topical and transdermal administration of therapeutic agents. The physicochemical constraints severely limit the number of molecules that can be considered as realistic candidates for transdermal delivery. Iontophoresis provides a mechanism to enhance the penetration of hydrophilic and charged molecules across the skin. The principal distinguishing feature is the control afforded by iontophoresis and the ability to individualize therapies. This may become significant as the impact of interindividual variations in protein expression and the effect on drug metabolism and drug efficacy is better understood. In this review we describe the underlying mechanisms that drive iontophoresis and we discuss the impact of key experimental parameters-namely, drug concentration, applied current and pH-on iontophoretic delivery efficiency. We present a comprehensive and critical review of the different therapeutic classes and molecules that have been investigated as potential candidates for iontophoretic delivery. The iontophoretic delivery of peptides and proteins is also discussed. In the final section, we describe the development of the first pre-filled, pre-programmed iontophoretic device, which is scheduled to be commercialized during the course of 2004.     

Intraoral drug delivery

The oral availability of many drugs is poor because of the pH of the stomach, the presence of enzymes, and extensive first-pass metabolism. Traditionally, these drugs have been administered as parenteral drug delivery systems, which invariably leads to poor patient compliance. This has made the pharmaceutical industry look for alternative routes of drug delivery. One possible route is via the oral cavity. This review compares the many different and novel drug delivery systems that have been developed for absorption through the oral cavity as well as those that undergo quick disintegration or dissolution in the oral cavity. Systems for oral delivery include mucoadhesive patches, films and tablets, as well as quick-disintegrating wafers, tablets and films. There are many examples of drugs that have been formulated into intraoral absorptive drug delivery systems as well as quick-disintegrating drug delivery systems. The fact that most of the research being conducted on intraoral drug delivery systems is driven by pharmaceutical manufacturers demonstrates the need for such drug delivery systems. As we begin to discover more about oral mucosal drug delivery, and develop much more sophisticated drug delivery systems, many more drugs will be formulated as intraoral systems. There is no doubt that the need for these systems is real, and many classes of drugs could benefit from this noninvasive type of drug delivery. The challenge now is to synthesize drug moieties that exhibit increased absorption across the oral mucosa and are more potent in their action. Intraoral drug delivery systems are possibly one of the very few drug delivery systems that seem to be ahead of the development of new drug compounds that are effectively absorbed across tissue membranes.     

Targeted drug delivery

Creating effective targeted drug delivery strategies is an integral component of the overall process of drug development. The four key requirements of an effective drug delivery system are retain, evade, target and release. Increasing the therapeutic index (TI) of a delivered compound by selectively delivering it to target areas is a goal that has many obstacles. Some of these concerns have been addressed by recent developments in areas such as liposomes, prodrugs, external targeting, controlled gene expression and antibodies. An analysis of some of the relevant inventions is discussed below. In order to present these inventions in a new light, materials science and engineering approaches have been used to examine the patents and help discuss their advantages and disadvantages. Patents concerning the manipulation of genes and proteins are at the core of this research and are an integral part of its future. Very specific targeting is possible when working at this level. The most exciting developments combine targeting strategies for delivery systems with many layers of specificity, increasing their targeting potential. It is also important to understand (and possibly exploit) the area to which a delivery system is being targeted and to learn from nature’s own delivery systems. Examples of these systems, including the red blood cell, the neutrophil and the secretory granule, are discussed using a materials engineering approach. This analysis reveals numerous characteristics that nature has designed into its delivery systems, and how these are important when creating man-made products. Working with these kinds of ideas, a true ‘magic bullet’ may be discovered.