The value and limitations of transgenic mouse models used in drug discovery for Alzheimer's disease: an update

Introduction: The exponential growth in the world's aged population has increased pressure on drug discovery efforts to identify innovative therapies for Alzheimer's disease (AD). The long and uncertain clinical trial path utilized to test the potential efficacy of these novel agents is challenging. For these and other reasons, there has been an explosion in the generation and availability of transgenic mouse models that mimic some, but not all aspects of AD. The largely overwhelmingly positive results obtained when testing potential clinical agents in these same animal models have failed to translate into similar positive clinical outcomes.

Areas covered: This review discusses the value and limitations associated with currently available transgenic mouse models of AD. Furthermore, the article proposes ways in which researchers can better characterize pharmacodynamic and pharmacokinetic endpoints to increase the success rate for novel therapies advancing into clinical development. Lastly, the author discusses ways in which researchers can supplement, expand and improve transgenic mouse models used in AD drug discovery.

Expert opinion: The use of transgenic mouse models that recapitulate various aspects of AD has expanded our knowledge and understanding of disease pathogenesis immensely. Further success in testing and translating novel therapies from animal models into bona fide medicines would be enhanced by i) the availability of better models that more fully recapitulate the disease spectrum, ii) defining and measuring standardized endpoints that display a pharmacodynamic range, iii) building and including translatable biomarkers and iv) including novel endpoints that would be expected to translate into clinically beneficial outcomes.     

Developing models for cachexia and their implications in drug discovery

Introduction: Cachexia is a complex metabolic syndrome associated with underlying illness and characterized by loss of muscle with or without loss of fat mass. Systemic inflammation plays a central role in its pathophysiology. As millions of patients are in a cachectic state of chronic disease, cachexia is one of the major causes of death worldwide. Difficulties in the recruitment and follow-up of clinical trials mean that well-characterized animal models are of great importance in developing cachexia therapies. However, some of the widely used animal models have limitations in procedural reproducibility or in recapitulating in the cachectic phenotype, which has warranted the development of novel models for cachexia.

Areas covered: This review focuses on some of the currently developing rodent models designed to mimic each co-morbidity in cachexia.

Expert opinion: Through developing cancer models, researchers have been seeking more targets for intervention. In cardiac cachexia, technical issues have been overcome by transgenic models. Furthermore, the development of new animal models has enabled the elucidation of the roles of inflammation, anabolism/catabolism in muscle/fat tissue and anorexia on cachexia. As metabolic and inflammatory pathways in cachexia may compromise cardiac muscle, the analysis of cardiac function/tissue in non-cardiac cachexia may be a useful component of cachexia assessment common to different underlying diseases and pave the way for novel drug discovery.     

Models and screening assays for drug discovery in osteoporosis

Importance of the field: Osteoporosis affects nearly 100 million people in Europe, Japan and the US, and the number is increasing due to aging of the population. Preclinical efficacy studies performed according to regulatory guidelines are large, long and expensive, and there is a need for guidance and recommendations on how to perform preliminary studies prior to the regulatory studies.

Areas covered in this review: We review research models that can be used for preclinical efficacy testing of new drug candidates for osteoporosis. Our focus is on testing compounds targeted to directly decrease osteoclastic bone resorption or increase osteoblastic bone formation.

What the reader will gain: We provide an overview of in vitro bone cell culture systems and osteoporosis animal models useful for preclinical efficacy studies and a step-by-step approach on how the most interesting compound can be selected from thousands of drug candidates. Different approaches for testing anti-catabolic and anabolic compounds are provided.

Take home message: Efficacy of new osteoporosis drug candidates can be first proven conveniently using in vitro bone cell cultures and then confirmed in short-term animal studies, followed by more extensive animal studies, and finally a regulatory study performed according to the guidelines of regulatory authorities.     

Nanocarrier-based topical drug delivery for the treatment of skin diseases

Introduction: Skin disorders will continue to cause complications in patients. At present, there is an expansion of research into dermatologic treatment due to a critical need for new treatment options to treat skin diseases.

Areas covered: The skin itself provides a natural barrier against particle penetration for topical delivery. However, it also offers a potential approach for the delivery of therapeutics, especially in diseased skin and via the openings of hair follicles. Recent innovation might be achieved in the field of dermatological treatment with improvement in the dermal localization of bioactives into the affected skin region, via novel nanocarriers that deliver the drugs directly to the target cells. After application, these nanocarriers can penetrate through the stratum corneum into viable skin and accumulate at the target site. However, noteworthy uptake does occur after damage and in certain diseased skin.

Expert opinion: Skin-targeted topical delivery by means of nanosystems, in order to produce sustained release and maintain a localized effect, will result in an effective treatment of various life-threatening dermatological conditions. In addition, research continues into the interactions between novel particles, skin and skin lipid, and the influence of particle composition on drug distribution within the skin strata.     

Animal models for acute radiation syndrome drug discovery

Introduction: Although significant scientific advances have been made over the past six decades in developing safe, nontoxic and effective radiation/medical countermeasures (MCMs) for acute radiation syndrome (ARS), no drug has been approved by the US FDA. The availability of adequate animal models is a prime requisite under the criteria established by the FDA ‘animal rule’ for the development of novel MCMs for ARS and the discovery of biomarkers for radiation exposure.

Areas covered: This article reviews the developments of MCMs to combat ARS, with particular reference to the various animal models (rodents: mouse and rat; canine: beagle; minipigs and nonhuman primates [NHPs]) utilized for the in-depth evaluation. The objective, pathways and challenges of the FDA Animal Efficacy Rule are also discussed.

Expert opinion: There are a number of well-defined animal models, the mouse, canine and NHP, that are being used for the development of MCMs. Additional animal models, such as the minipig, are under development to further assist in the identification, efficacy testing and approval of MCMs under the FDA Animal Efficacy Rule.     

Orthotopic mouse models expressing fluorescent proteins for cancer drug discovery

Importance of the field: Currently used rodent tumor models, including transgenic tumor models, or subcutaneously growing human tumors in immunodeficient mice, do not sufficiently represent clinical cancer, especially with regard to metastasis and drug sensitivity.

Areas covered in this review: To obtain clinically accurate models, we have developed the technique of surgical orthotopic implantation (SOI) to transplant histologically intact fragments of human cancer, including tumors taken directly from the patient, to the corresponding organ of immunodeficient rodents. SOI allows the growth and metastatic potential of the transplanted tumors to be expressed and reflects clinical cancer of all types. Effective drugs can be discovered and evaluated in the SOI models utilizing human tumor cell lines and patient tumors. Visualization of many aspects of cancer initiation and progression in vivo has been achieved with fluorescent proteins. Tumors and metastases in the SOI models that express fluorescent proteins can be visualized noninvasively in intact animals, greatly facilitating drug discovery.

What the reader will gain: This review will provide information on the imageable mouse models of cancer that are clinically relevant, especially regarding metastasis and their use for drug discovery and evaluation.

Take home message: SOI mouse models of cancer reproduce the features of clinical cancer.     

Topical drug delivery systems in dermatology: a review of patient adherence issues

Introduction: Until now, the main focus of medication adherence research has been oral drugs. Fewer studies have examined adherence to topical drugs. The issue of patient adherence to topical drugs is particularly significant in relation to chronic skin diseases, including psoriasis, atopic dermatitis, and acne, which require long-term use of topical medications.

Areas covered: The authors reviewed the current evidence of adherence to topical therapy in dermatological diseases, mainly focusing on psoriasis, atopic dermatitis, and acne. The predictors or factors influencing adherence to topical therapy are then discussed. In general, the prevalence of poor adherence to topical drugs is high in dermatology. However, this research area remains empirically underdeveloped. We are still facing challenges in measuring topical medication adherence.

Expert opinion: The authors recommend some possible ways to improve topical medication adherence and provide some future research directions. Taking patient preference into consideration in selecting the right topical delivery vehicle is particularly important in improving patient adherence. Better drug design, formulation, or technology may be another important direction. Other possible effective ways to improve topical medication adherence include good physician–patient relationship, patient education, individualized treatment plan, psychological intervention, electronic devices, and return visits.     

Drug discovery in prostate cancer mouse models

Introduction: The mouse is an important, though imperfect, organism with which to model human disease and to discover and test novel drugs in a preclinical setting. Many experimental strategies have been used to discover new biological and molecular targets in the mouse, with the hopes of translating these discoveries into novel drugs to treat prostate cancer in humans. Modeling prostate cancer in the mouse, however, has been challenging, and often drugs that work in mice have failed in human trials.

Areas covered: The authors discuss the similarities and differences between mice and men; the types of mouse models that exist to model prostate cancer; practical questions one must ask when using a mouse as a model; and potential reasons that drugs do not often translate to humans. They also discuss the current value in using mouse models for drug discovery to treat prostate cancer and what needs are still unmet in field.

Expert opinion: With proper planning and following practical guidelines by the researcher, the mouse is a powerful experimental tool. The field lacks genetically engineered metastatic models, and xenograft models do not allow for the study of the immune system during the metastatic process. There remain several important limitations to discovering and testing novel drugs in mice for eventual human use, but these can often be overcome. Overall, mouse modeling is an essential part of prostate cancer research and drug discovery. Emerging technologies and better and ever-increasing forms of communication are moving the field in a hopeful direction.     

Occupational skin diseases in automotive industry workers

Context: Studies on occupational skin diseases in workers of the automotive industry are few.

Aim: To investigate the prevalence of occupational skin diseases in workers of the automotive industry.

Materials and methods: Between September and December 2011, a total of 405 workers from the automotive repair industry in Diyarbak?r were interviewed. They were active workers in the repair industry who had been employed for at least six months. Business owners, sellers of spare parts and accounting officers were not included. The employees were examined at their workplaces and the working conditions were observed. Detailed dermatological examination was performed.

Results: The mean age of the 405 workers who participated in the study was 27.7?±?10.3. The mean working time of employees was 13.3?±?10.4 years. All of the employees were male. Dermatological diseases were not detected in 144 out of 405 workers (35.6%) and at least one condition was diagnosed in 261 (64.4%). The most frequent diagnosis was callus, hyperkeratosis, clavus (27.7%), followed by nail changes (16.8%) and superficial mycoses (12.1%). Contact dermatitis was seen at a rate of 5.9%.

Discussion: Traumatic lesions such as hyperkeratotic lesions and nail changes were found most frequently. Traumatic lesions were common among individuals who did not use gloves. Most nail changes were localized leuconychia, a finding not reported in the studies on automotive industry workers. In accordance with the literature, irritant contact dermatitis was observed in patients with a history of atopy and who had been working for a long time.

Conclusion: Occupational skin diseases comprise an important field in dermatology, deserving much attention. Further studies on occupational dermatology are necessary.     

Colorectal cancer models for novel drug discovery

Introduction: Despite increased screening rates and advances in targeted therapy, colorectal cancer (CRC) remains the third leading cause of cancer-related mortality. CRC models that recapitulate key features of human disease are essential to the development of novel and effective therapeutics. Classic methods of modeling CRC such as human cell lines and xenograft mice, while useful for many applications, carry significant limitations. Recently developed in vitro and in vivo models overcome some of these deficiencies and thus can be utilized to better model CRC for mechanistic and translational research.

Areas covered: The authors review established models of in vitro cell culture and describe advances in organoid culture for studying normal and malignant intestine. They also discuss key features of classic xenograft models and describe other approaches for in vivo CRC research, including patient-derived xenograft, carcinogen-induced, orthotopic transplantation and transgenic mouse models. We also describe mouse models of metastatic CRC.

Expert opinion: No single model is optimal for drug discovery in CRC. Genetically engineered models overcome many limitations of xenograft models. Three-dimensional organoids can be efficiently derived from both normal and malignant tissue for large-scale in vitro and in vivo (transplantation) studies and are thus a significant advance in CRC drug discovery.     

Animal models in tuberculosis research – where is the beef?

Introduction: Tuberculosis (TB) is a major global health problem, and new drugs and vaccines are urgently needed. As clinical trials in humans require tremendous resources, preclinical drug and vaccine development largely relies on valid animal models that recapitulate the pathology of human disease and the immune responses of the host as closely as possible.

Areas covered: This review describes the animal models used in TB research, the most widely used being mice, guinea pigs and nonhuman primates. In addition, rabbits and cattle provide models with a disease pathology resembling that of humans. Invertebrate models, including the fruit fly and the Dictyostelium amoeba, have also been used to study mycobacterial infections. Recently, the zebrafish has emerged as a promising model for studying mycobacterial infections. The zebrafish model also facilitates the large-scale screening of drug and vaccine candidates.

Expert opinion: Animal models are needed for TB research and provide valuable information on the mechanisms of the disease and on ways of preventing it. However, the data obtained in animal studies need to be carefully interpreted and evaluated before making assumptions concerning humans. With an increasing understanding of disease mechanisms, animal models can be further improved to best serve research goals.     

Mouse models in squamous cell lung cancer: impact for drug discovery

Introduction: Squamous cell lung cancer (SQCLC) is the second most common subtype of non-small cell lung cancer (NSCLC) and has limited therapeutic options. Its development is likely a result of a multistep process in response to chronic tobacco exposure, involving sequential metaplasia, dysplasia and invasive carcinoma. Its complex genomic landscape has recently been revealed but no driver mutations have been validated that could lead to molecularly targeted therapy as have emerged in lung adenocarcinoma. Few preclinical murine models exist for testing and developing novel therapeutics in SQCLC.

Areas covered: This review discusses the pathophysiology and molecular underpinnings of SQCLC that have limited the development of animal models. It then explores the advantages and limitations of a variety of existing mouse models and illustrates their potential application in drug discovery and chemoprevention.

Expert opinion: There are several challenges in the development of mouse models for SQCLC, such as lack of validated driver genetic alterations, unclear cell of origin, and difficulty in reproducing the sophisticated tumor microenvironment of human disease. Nevertheless, several successful SQCLC murine models have emerged, especially Patient Derived Xenografts (PDXs) and Genetically Engineered Mouse Models (GEMMs). Continued efforts are needed to generate more SQCLC animal models to better understand its carcinogenesis and metastasis and to further test novel therapeutic strategies.     

Rodent models for Alzheimer’s disease drug discovery

Introduction: Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by memory loss and personality changes, leading to dementia. Histopathological hallmarks are represented by aggregates of beta-amyloid peptide (Aβ) in senile plaques and deposition of hyperphosphorylated tau protein in neurofibrillary tangles in the brain. Rare forms of early onset familial Alzheimer’s disease are due to gene mutations. This has prompted researchers to develop genetically modified animals that could recapitulate the main features of the disease. The use of these models is complemented by non-genetically modified animals.

Areas covered: This review summarizes the characteristics of the most used transgenic (Tg) and non-Tg models of AD. The authors have focused on models mainly used in their laboratories including amyloid precursor protein (APP) Tg2576, APP/presenilin 1, 3xAD, single h-Tau, non-Tg mice treated with acute injections of Aβ or tau, and models of physiological aging.

Expert opinion: Animal models of disease might be very useful for studying the pathophysiology of the disease and for testing new therapeutics in preclinical studies but they do not reproduce the entire clinical features of human AD. When selecting a model, researchers should consider the various factors that might influence the phenotype. They should also consider the timing of testing/treating animals since the age at which each model develops certain aspects of the AD pathology varies.     

Animal models for anti-emphysema drug discovery

Introduction: Emphysema is characterized by an abnormal and permanent enlargement of airspaces accompanied by destruction of their walls. Up to now, there is no cure for emphysema, and animal models may be important for new drug discovery.

Areas covered: Herein, the authors review animal models of emphysema since the protease-antiprotease hypothesis as well as the results obtained with compounds tested in these models. Of particular importance are animal models of cigarette smoke exposure since it is the most important risk factor of emphysema. The authors also analyze two approaches to drug testing, that is, the approach aimed at preventing emphysema and the one aimed at reversing it.

Expert opinion: It has been suggested that early and late interventions do not have the same protective effect and that late interventions are much more likely to reveal treatments beneficial in humans. However, this is not always the case, and a compound that prevents emphysema when administered as an early intervention can also have the same protective effect when given as a late intervention. Furthermore, the fact that a compound detected by means of early intervention is now in clinical practice shows that early intervention studies can be predictive for efficacy in humans.     

Development of transplant immunosuppressive agents – considerations in the use of animal models

ABSTRACT

Introduction: The development of all immunosuppressant agents to date has involved the experimental use of large and small animal models. Over the last half-century, immunosuppressive drugs have extended the lives of transplant patients worldwide. However, the use of animal models in the development of these drugs is not perfect, and this has brought to light a number of issues including idiosyncratic reactions that are found in animal models but not in humans. The 2006 highly publicized case of the ‘elephant man’ TGN 1412 drug trial highlights the importance of being cogent of the limitations of animal models.

Areas covered: This review covers the utility and limitations of the use of animal models for the development of immunosuppressant agents. This includes both large and small animal models, particularly rodent models in the transplant setting.

Expert opinion: The use of animal models represents a critical stage in the development of immunosuppressive drugs. Limitations include physiological differences to humans; this is especially true of immunologically naïve lab rodents with small memory cell populations. Toxic drug levels may differ widely between species. Animal models are also costly and raise ethical concerns. However, there is currently no way to recreate the complex environment of the human immune system purely in vitro.     

Resolvin inflammation with pain

Background: Inflammation and pain coexist in conditions such as arthritis, inflammatory bowel disease and lower back pain. The drugs currently used to treat the combination of inflammation and pain all have disadvantages. Thus, new drugs and new approaches are needed to treat inflammation with pain. Resolvins are considered to be part of the natural resolving mechanism for inflammation and have been shown to prevent inflammation in animal models.

Objectives/methods: To evaluate a paper suggesting that the resolvins RvE1 and RvD1 attenuate inflammatory pain in animal models.

Results: RvE1 has been shown to attenuate inflammation and, to a lesser extent, pain in animal models. Limited results are presented of the effectiveness of RvD1 against inflammatory pain.

Conclusion: Drugs that mimic or potentiate the effects of the resolvins may be useful for the treatment of some inflammation with pain.     

Novel nicotinamide skin-adhesive hot melt extrudates for treatment of acne

ABSTRACT

Objectives: Hot melt extrusion is a continuous process with wide industrial applicability. Till current date, there have been no reports on the formulation of extrudates for topical treatment of dermatological diseases.

Methods: The aim of the present work was to prepare and characterize medicated hot melt extrudates based on Soluplus polymer and nicotinamide, and to explore their applicability in acne treatment. The extrudates were characterized using DSC, FTIR, XRD, and DVS. The extrudates were also tested for their skin adhesion potential, ability to deposit nicotinamide in different skin layers, and their clinical efficacy in acne patients.

Results: The 10% nicotinamide extrudates exhibited amorphous nature which was reserved during storage, with no chemical interaction between nicotinamide and Soluplus. Upon contrasting the skin adhesion and drug deposition of extrudates and nicotinamide gel, it was evident that the extrudates displayed significantly higher adhesion and drug deposition reaching 4.8 folds, 5.3 folds, and 4.3 folds more in the stratum corneum, epidermis and dermis, respectively. Furthermore, the extrudates significantly reduced the total number of acne lesions in patients by 61.3% compared to 42.14% with the nicotinamide gel.

Conclusion: Soluplus extrudates are promising topical drug delivery means for the treatment of dermatological diseases.     

Transgenic animals expressing human immunoglobulin genes

Patent Summary

Methods for the production of transgenic animals expressing immunoglobulin genes from another animal are described. This could lead to the specific production of, for example, human antibodies of various classes in non-human animals such as mice or farm animals. The antibodies could be used in humans for therapy of cancer and other diseases or to alter physiological states in humans.

The transgenic animals were constructed to have targeted insertions of the desired immunoglobulin genes into the homologous place in the mouse genome. The heavy and light chains were sequentially constructed and a minilocus inserted into a mouse zygote where it recombines at the correct locus. In one example unrearranged human heavy chains were introduced into the genome of the mouse which then functionally rearranged the genes. Also described is the use of antisense RNA to functionally block the expression of the endogenous mouse immunoglobulin genes.