Screening methods for influenza antiviral drug discovery

Introduction: Influenza antiviral high-throughput screens have been extensive, and yet no approved influenza antivirals have been identified through high-throughput screening. This underscores the idea that development of successful screens should focus on the exploitation of the underrepresented viral targets and novel, therapeutic host targets.

Areas covered: The authors review conventional screening applications and emerging technologies with the potential to enhance influenza antiviral discovery. Real-world examples from the authors' work in biocontained environments are also provided. Future innovations are discussed, including the use of targeted libraries, multiplexed assays, proximity-based endpoint methods, non-laboratory-adapted virus strains, and primary cells, for immediate physiological relevance and translational applications.

Expert opinion: The lack of successful anti-influenza drug discovery using high-throughput screening should not deter future efforts. Increased understanding of the functions of viral targets and host–pathogen interactions has broadened the target reservoir. Future screening efforts should focus on identifying new drugs against unexploited viral and host targets using currently developed assays, and on the development of novel, innovative assays to discover new drugs with novel mechanisms. Innovative screens must be designed to identify compounds that specifically inhibit protein–protein or protein–RNA interactions or other virus/host factor interactions that are crucial for viral replication. Finally, the use of recent viral isolates, increased biocontainment (for highly-pathogenic strains), primary cell lines, and targeted compound libraries must converge in efficient high-throughput primary screens to generate high-content, physiologically-relevant data on compounds with robust antiviral activity.     

Models of retinal diseases and their applicability in drug discovery

Introduction: The impact of vision debilitating diseases is a global public health concern, which will continue until effective preventative and management protocols are developed. Two retinal diseases responsible for the majority of vision loss in the working age adults and elderly populations are diabetic retinopathy (DR) and age-related macular degeneration (AMD), respectively. Model systems, which recapitulate aspects of human pathology, are valid experimental modalities that have contributed to the identification of signaling pathways involved in disease development and consequently potential therapies.

Areas covered: The pathology of DR and AMD, which serve as the basis for designing appropriate models of disease, is discussed. The authors also review in vitro and in vivo models of DR and AMD and evaluate the utility of these models in exploratory and pre-clinical studies.

Expert opinion: The complex nature of non-Mendelian diseases such as DR and AMD has made identification of effective therapeutic treatments challenging. However, the authors believe that while in vivo models are often criticized for not being a ‘perfect’ recapitulation of disease, they have been valuable experimentally when used with consideration of the strengths and limitations of the experimental model selected and have a place in the drug discovery process.     

Future prospects in antiviral therapy

Two important stumbling blocks to the development of effective and nontoxic antiviral drugs are the intracellular localization of the virus and the fact that a virus uses host cell functions to multiply. Therefore, new antiviral drugs must act on a virus-specific function. Most currently available useful antiviral drugs are the result of compound screening of large numbers of possible agents. Advances in our understanding of the molecular biology and biochemistry of the viral multiplication cycle and new laboratory techniques for determining the molecular sites of action have now made it possible to develop and screen new antiviral drugs in a more purposeful manner. Another possible option in antiviral therapy is combination therapy using drugs that enhance the therapeutic effect or diminish side-effects. The most promising new antiviral drugs are discussed according to the different steps they affect in the viral multiplication process. Combination therapy is also reviewed.     

Broad-spectrum coronavirus antiviral drug discovery

Introduction: The highly pathogenic coronaviruses severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) are lethal zoonotic viruses that have emerged into human populations these past 15 years. These coronaviruses are associated with novel respiratory syndromes that spread from person-to-person via close contact, resulting in high morbidity and mortality caused by the progression to Acute Respiratory Distress Syndrome (ARDS).

Areas covered: The risks of re-emergence of SARS-CoV from bat reservoir hosts, the persistence of MERS-CoV circulation, and the potential for future emergence of novel coronaviruses indicate antiviral drug discovery will require activity against multiple coronaviruses. In this review, approaches that antagonize viral nonstructural proteins, neutralize structural proteins, or modulate essential host elements of viral infection with varying levels of efficacy in models of highly pathogenic coronavirus disease are discussed.

Expert opinion: Treatment of SARS and MERS in outbreak settings has focused on therapeutics with general antiviral activity and good safety profiles rather than efficacy data provided by cellular, rodent, or nonhuman primate models of highly pathogenic coronavirus infection. Based on lessons learned from SARS and MERS outbreaks, lack of drugs capable of pan-coronavirus antiviral activity increases the vulnerability of public health systems to a highly pathogenic coronavirus pandemic.     

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.     

抗病毒药物的用药量及要求分析

目的分析笔者所在医院抗病毒药物的用药量及要求,以探讨抗病毒药物的合理使用。方法随机选取医院皮肤科、儿科、内科、传染科门诊及眼科5个科室2009年1月～2012年1月的处方2000张,对其中抗病毒药物进行用药量分析。结果通过计算各类药物使用频率及药物利用指数得出,抗病毒类药物中核苷类药物的使用量较大,排序靠前的拉米夫定、阿昔洛韦、更昔洛韦、泛昔洛韦等均为核苷类药物,药物用量基本控制在合理使用范围。结论笔者所在医院抗病毒药物的使用基本控制在合理使用范围,但仍出现用药量偏大现象,需要引起重视和加以改进。     

Challenges with in vitro and in vivo experimental models of urinary bladder cancer for novel drug discovery

ABSTRACT

Introduction: Urinary bladder cancer (UBC) is the second most frequent malignancy of the urinary system and the ninth most common cancer worldwide, affecting individuals over the age of 65. Several investigations have embarked on advancing knowledge of the mechanisms underlying urothelial carcinogenesis, understanding the mechanisms of antineoplastic drugs resistance and discovering new antineoplastic drugs. In vitro and in vivo models are crucial for providing additional insights into the mechanisms of urothelial carcinogenesis. With these models, various molecular pathways involved in urothelial carcinogenesis have been discovered, allowing therapeutic manipulation.

Areas covered: This paper provides critical information on existing in vitro and in vivo models to screen the efficacy and toxicity of innovative UBC therapies and point out the challenges for new and improved models.

Expert opinion: In our opinion, results obtained with in vitro and in vivo models should be interpreted together, as a set of delicate biological tools that can be used at different stages in the drug discovery process, to address specific questions. With the development of new technologies, new assays and biomarkers are going to play an important role in the study of UBC. The molecular diagnostics and genomic revolution will not only help to develop new drug therapies, but also to achieve tailored therapies.     

New approaches for pediatric rhabdomyosarcoma drug discovery: targeting combinatorial signaling

Introduction: Rhabdomyosarcomas (RMS) are rare heterogeneous pediatric tumors that are treated by surgery, chemotherapy and irradiation. New therapeutic approaches are needed, especially in the advanced stages to target the pro-oncogenic signals. Exploring the molecular interactions of the regulatory signals and their roles in the developmental aspects of different subtypes of RMS is essential to identify potential targets and develop new therapeutic drugs.

Areas covered: Insights into different drug discovery approaches are discussed with specific emphasis on gene expression profiling, fusion protein, role of small interfering RNA (siRNA)- and microRNA (miRNA)-based discovery approaches, targeting cancer stem cells, and in vitro and in vivo model systems. Targeting some overexpressed signals along with the possibilities of combination therapy of validated drug targets is discussed. Additionally, methods to overcome the limitations of discovery-based research are briefly discussed.

Expert opinion: Due to drug resistance, ineffective therapy in advanced stages and relapse, there is a demand to explore new drug targets and discovery approaches. Implementing miRNA-based profiling would reveal the extent of miR-based regulation, various biomarkers and potential targets in RMS. A suitable combination of innovative techniques and the use of model systems might assist the identification and validation of novel targets and drug discovery methods. Combining specific drugs along with type-specific target inhibition of overexpressed mRNAs through siRNA approaches would enable the development of personalized therapy.     

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.     

Recent advances in antiviral agents: antiviral drug discovery for hepatitis viruses

Hepatitis B virus (HBV)- or hepatitis C virus (HCV)- associated liver diseases are now one of the important health problems in the world because of the high numbers of patients and the serious consequences. Recently, however, relatively effective treatments with antiviral agents have become available. Interferon (IFN), lamivudine and adefovir are now approved for treatment of HBV-associated liver diseases and they have been shown to be fairly effective. The goal of treatments for HBV-associated liver disease is to achieve a clinical cure in as short a period as possible without producing resistance mutation of the virus. Several nucleotide analogues with more potent antiviral activities are now in clinical trials. In the case of HCV-associated liver diseases, Pegylated IFN (Peg IFN) + ribavirin combination therapy is the standard and most effective treatment with a sustained response of 60-70%. The goal of the treatments for these liver diseases is to induce the complete eradication of the infected virus and at present new anti HCV drugs targeting the molecular segments of the virus are under development. It is expected that the complete eradication of infected virus will be possible in most cases in the near future.     

Efficacy of repurposed antiviral drugs: Lessons from COVID-19

The clinical, social, and economic impacts of the coronavirus disease 2019 (COVID-19) pandemic, originated by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have motivated a massive search and investment to find treatments for this new disease. Repurposing drugs has been an appealing strategy for the rapid translation of in vitro and ex vivo drug discovery to the clinic. Several repurposed drugs have been assessed clinically, but no effective repurposed antiviral has been identified so far. Of note, no effective treatments for COVID-19 or for any other viral disease have been found by repurposing drugs identified through hypothesis-free screens. Here, I discuss whether drug repurposing is the best strategy for developing effective therapies to eradicate COVID-19 and other viral human infections.     

Experimental models for anxiolytic drug discovery in the era of omes and omics

Introduction: Animal behavioral models have become an indispensable tool for studying anxiety disorders and testing anxiety-modulating drugs. However, significant methodological and conceptual challenges affect the translational validity and accurate behavioral dissection in such models. They are also often limited to individual behavioral domains and fail to target the disorder's real clinical picture (its spectrum or overlap with other disorders), which hinder screening and development of novel anxiolytic drugs.

Areas covered: In this article, the authors discuss and emphasize the importance of high-throughput multi-domain neurophenotyping based on the latest developments in video-tracking and bioinformatics. Additionally, the authors also explain how bioinformatics can provide new insight into the neural substrates of brain disorders and its benefit for drug discovery.

Expert opinion: The throughput and utility of animal models of anxiety and other brain disorders can be markedly increased by a number of ways: i) analyzing systems of several domains and their interplay in a wider spectrum of model species; ii) using a larger number of end points generated by video-tracking tools; iii) correlating behavioral data with genomic, proteomic and other physiologically relevant markers using online databases and iv) creating molecular network-based models of anxiety to identify new targets for drug design and discovery. Experimental models utilizing bioinformatics tools and online databases will not only improve our understanding of both gene–behavior interactions and complex trait interconnectivity but also highlight new targets for novel anxiolytic drugs.     

New developments in flavivirus drug discovery

ABSTRACT

Introduction: Flaviviruses are major causes of infectious disease. The vast global, social and economic impact due to morbidity and mortality associated with diseases caused by these viruses urgently demands effective therapeutic interventions. There is currently no specific antiviral therapy available for the effective clinical treatment of infections by any of the flaviviridae. Development of more effective vaccines and antiviral agents for the prevention and treatment of most flavivirus infections remains a clear public health priority in the 21st century.

Areas covered: This review describes some of the recent discoveries in the field of flavivirus inhibitor development, with a particular focus on targeting viral proteins. Emphasis is placed on the advances published during the 2012–2015 period.

Expert opinion: The field of drug discovery targeting viral proteins has progressed slowly in recent years. New information, particularly on structures, location and mechanisms of action of established protein targets have been reported. There have also been studies on repurposing known drugs as templates for targeting flavivirus proteins and these hits could be promising templates for developing new more potent inhibitors. Further research should be conducted to improve in vitro assays that better reflect the conditions found in cellular environments.     

抗病毒药物耐药及耐药机制研究进展

目前临床应用的抗病毒药物达40多种，为病毒引起的疾病的治疗发挥了重大作用。与临床其他抗感染药物一样，抗病毒药物长期应用易产生耐药性．降低疗效，成为临床治疗及新药开发的重要问题。本文就抗艾滋病毒药物、抗乙型肝炎病毒药物、抗流感病毒药物及抗疱疹病毒药物耐药性及耐药机制研究进行综述。     

Animal models of skin disease for drug discovery

Introduction: Discovery of novel drugs, treatments, and testing of consumer products in the field of dermatology is a multi-billion dollar business. Due to the distressing nature of many dermatological diseases, and the enormous consumer demand for products to reverse the effects of skin photodamage, aging, and hair loss, this is a very active field.

Areas covered: In this paper, we will cover the use of animal models that have been reported to recapitulate to a greater or lesser extent the features of human dermatological disease. There has been a remarkable increase in the number and variety of transgenic mouse models in recent years, and the basic strategy for constructing them is outlined.

Expert opinion: Inflammatory and autoimmune skin diseases are all represented by a range of mouse models both transgenic and normal. Skin cancer is mainly studied in mice and fish. Wound healing is studied in a wider range of animal species, and skin infections such as acne and leprosy also have been studied in animal models. Moving to the more consumer-oriented area of dermatology, there are models for studying the harmful effect of sunlight on the skin, and testing of sunscreens, and several different animal models of hair loss or alopecia.     

Minipigs as models in drug discovery

ABSTRACT

Introduction: Influenza continues to be a major public health concern. Antivirals play an important role in limiting the burden of disease and preventing infection and/or transmission. The developments of such agents are heavily dependent on pre-clinical evaluation where animal models are used to answer questions that cannot be easily addressed in human clinical trials. There are numerous animal models available to study the potential benefits of influenza antivirals but each animal model has its own pros and cons.

Areas covered: In this review, the authors describe the advantages and disadvantages of using mice, ferrets, guinea pigs, cotton rats, golden hamsters and non-human primates to evaluate influenza therapeutics.

Expert opinion: Animals used for evaluating influenza therapeutics differ in their susceptibility to influenza virus infection, their ability to display clinical signs of illness following viral infection and in their practical requirements such as housing. Therefore, defining the scientific question being asked and the data output required will assist in selecting the most appropriate animal model.