Preclinical drug development for childhood cancer

Importance of the field: More effective drugs are needed to treat poor prognosis paediatric malignancies. Development of anticancer agents for childhood cancers faces several unique challenges compared with their adult counterparts.

Areas covered in this review: We demonstrate how recent advances in preclinical drug development may overcome these difficulties and challenges. We explain the role of academia, regulators and industry in this field, address issues with preclinical models and illustrate several examples of biology-driven drug development in childhood cancers.

What the reader will gain: Increased knowledge about preclinical drug development in paediatric oncology including different preclinical models, established preclinical research networks, and relationships among academia, industry and regulators, as illustrated by several examples of targeted agents in childhood solid malignancies.

Take home message: It is anticipated that emerging advanced preclinical models and testing platforms will provide a more efficient, biologically-driven rationale to support the use of targeted therapies in several malignancies such as neuroblastoma, medulloblastoma or high grade glioma which account for the majority of deaths related to childhood cancer.     

Structure-based drug design for hypoxia-inducible factor prolyl-hydroxylase inhibitors and its therapeutic potential for the treatment of erythropoiesis-stimulating agent-resistant anemia: raising expectations for exploratory clinical trials

Introduction: Anemia occurs in various chronic diseases and its treatment is dramatically improved after the appearance of erythropoiesis-stimulating agents (ESA). However, there are several problems regarding the use of ESA including: i) invasiveness, ii) high cost and iii) ESA resistance. Therefore, there is a need to develop small molecule drugs which can improve these problems. Hypoxia-inducible factor (HIF) plays a key role in regulating erythropoietin production. HIF stabilizers, particularly, prolyl hydroxylase domain-containing protein (PHD) inhibitors, have emerged as small molecule-based anti-anemia medicine.

Areas covered: This article discusses the current status of PHD inhibitors and the pros and cons of currently tested methods. Specifically, the article reviews the advantages of structure-based drug design in the development of PHD inhibitors and looks at future perspectives within the field.

Expert opinion: Despite the fact that structure-based drug design has dramatically improved drug discovery, testing on humans is still one of the most time-consuming parts of drug discovery and one that is not accelerated by structural approaches. Exploratory clinical trials, first-in-man studies have emerged as a new strategy for preclinical and clinical development of drugs. Exploratory clinical trials will not only reduce the time and cost in preclinical trials but also provide important information on candidate drug's pharmacological effects in humans. Exploratory clinical trials may be a potential alternative strategy for the drug discovery in the future.     

Emerging neuroprotective drugs for the treatment of acute ischaemic stroke

Introduction: Neuroprotection aims to restrict the ischaemic damage following stroke by preventing salvageable neurons from dying. Despite successes in experimental stroke studies, neuroprotective strategies have failed in clinical trials so far. Nevertheless, promising neuroprotective drugs are currently being investigated in clinical trials.

Areas covered: This review provides an overview of the existing treatment of acute ischaemic stroke, discusses current research goals and puts special emphasis on emerging neuroprotective drugs. The authors systematically searched the database Clinicaltrials.gov for ongoing Phase II and Phase III clinical trials of neuroprotective drugs for acute ischaemic stroke. Mechanisms of action of these candidate neuroprotectants and the results of preceding preclinical studies and clinical pilot trials are described.

Expert opinion: In order to facilitate a successful translation from bench to bedside, future experimental studies should follow rigorous quality standards. Recent concepts to overcome the translation roadblock include the implementation of multicentre preclinical Phase III studies, the use of stroke models in non-human primates and the introduction of a preclinical trial registration.     

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.     

A retrospective review of the progress in amyotrophic lateral sclerosis drug discovery over the last decade and a look at the latest strategies

Introduction: Drug discovery for amyotrophic lateral sclerosis (ALS) has experienced a surge in clinical studies and remarkable preclinical milestones utilizing a variety of mutant superoxide dismutase 1 model systems. Of the drugs that were tested and showed positive preclinical effects, none demonstrated therapeutic benefits to ALS patients in clinical settings.

Areas covered: This review discusses the advances made in drug discovery for ALS and highlights why drug development is proving to be so difficult. It also discusses how a closer look at both preclinical and clinical studies could uncover the reasons why these preclinical successes have yet to result in the availability of an effective drug for clinical use.

Expert opinion: Valuable lessons from the numerous preclinical and clinical studies supply the biggest advantage in the monumental task of finding a cure for ALS. Obviously, a single design type for ALS clinical trials has not yielded success. The authors suggest a two-pronged approach that may prove essential to achieve clinical efficacy in the identification of novel targets and preclinical testing in multiple models to identify biomarkers that can function in diagnostic, predictive and prognostic roles, and changes to clinical trial design and patient recruitment criteria. The advancement of technology and invention of more powerful tools will further enhance the above. This will give rise to more sophisticated clinical trials with consideration of a range of criteria from: optimum dose, route of delivery, specific biomarkers, pharmacokinetics, pharmacodynamics and toxicology to biomarkers, timing for trial and patients’ clinical status.     

Mathematical modeling for novel cancer drug discovery and development

Introduction: Mathematical modeling enables: the in silico classification of cancers, the prediction of disease outcomes, optimization of therapy, identification of promising drug targets and prediction of resistance to anticancer drugs. In silico pre-screened drug targets can be validated by a small number of carefully selected experiments.

Areas covered: This review discusses the basics of mathematical modeling in cancer drug discovery and development. The topics include in silico discovery of novel molecular drug targets, optimization of immunotherapies, personalized medicine and guiding preclinical and clinical trials. Breast cancer has been used to demonstrate the applications of mathematical modeling in cancer diagnostics, the identification of high-risk population, cancer screening strategies, prediction of tumor growth and guiding cancer treatment.

Expert opinion: Mathematical models are the key components of the toolkit used in the fight against cancer. The combinatorial complexity of new drugs discovery is enormous, making systematic drug discovery, by experimentation, alone difficult if not impossible. The biggest challenges include seamless integration of growing data, information and knowledge, and making them available for a multiplicity of analyses. Mathematical models are essential for bringing cancer drug discovery into the era of Omics, Big Data and personalized medicine.     

Improving efficiency of initial tests for efficacy in smoking cessation drug discovery

Introduction: One obstacle to rapid development of new smoking cessation medications is the inefficient early clinical evaluation of the efficacy of novel drugs, which inform us as to whether or not to proceed with the greater expense and time of more formal clinical trials. The vast majority of novel drugs fail to show efficacy for cessation only after substantial resources have been spent and, thus, are largely wasted.

Areas covered: The author reviews the general limitations in the current typical procedures for initial tests of cessation efficacy in novel drugs. Small, randomized clinical trials often have good validity but may have practical limitations in achieving adequate statistical power to test novel versus placebo treatment conditions. Lab tests of acute drug effects on abstinence symptoms, during brief enforced cessation periods, are practical but have limited clinical predictive validity.

Expert opinion: Initial efficacy testing may be more efficient if done using innovative crossover designs that evaluate brief ‘practice’ quit periods for both active and placebo treatments within the same smokers, recruiting those high in quit motivation. Because this approach would require far fewer subjects and a shorter duration of testing, results could be obtained more rapidly and inexpensively to indicate that a novel drug may, or may not, be sufficiently efficacious as to warrant the greater costs and time of formal randomized clinical trials.     

The failure of anxiolytic therapies in early clinical trials: what needs to be done

Introduction: Anxiety spectrum disorders (ASDs) are highly prevalent psychiatric illnesses that affect millions of people worldwide. Strongly associated with stress, common ASDs include generalized anxiety disorder, panic, social anxiety, phobias and drug-abuse-related anxiety. In addition to ASDs, several other prevalent psychiatric illnesses represent trauma/stressor-related disorders, such as post-traumatic stress disorder and acute stress disorder. Anxiolytic drugs, commonly prescribed to treat ASDs and trauma/stressor-related disorders, form a highly heterogenous group, modulating multiple neurotransmitters and physiological mechanisms. However, overt individual differences in efficacy and the potential for serious side-effects (including addiction and drug interaction) indicate a need for further drug development. Yet, over the past 50 years, there has been relatively little progress in the development of novel anxiolytic medications, especially when promising candidate drugs often fail in early clinical trials.

Areas covered: Herein, the authors present recommendations of the Task Force on Anxiolytic Drugs of the International Stress and Behavior Society on how to improve anxiolytic drug discovery. These recommendations cover a wide spectrum of aspects, ranging from methodological improvements to conceptual insights and innovation.

Expert opinion: In order to improve the success of anxiolytic drugs in early clinical trials, the goals of preclinical trials may need to be adjusted from a clinical perspective and better synchronized with those of clinical studies. Indeed, it is important to realize that the strategic goals and approaches must be similar if we want to have a smoother transition between phases.     

A review of in vitro and in vivo models of oesophageal and gastric cancer

Importance of the field: Oesophageal and gastric cancers are leading causes of cancer-related mortality. In the era of targeted therapy and individualized treatment strategies, novel treatments for upper-gastrointestinal cancers are only just emerging compared to significant advances in other solid tumour types such as colorectal, breast and lung cancers. Clinical trials are investigating the value of established targeted agents for the treatment of oesophageal and gastric malignancies; however none are used in routine clinical practice.

Areas covered in this review: In this review we have looked at current in vitro and in vivo models of oesophageal and gastric cancers which may improve our understanding of the biology of these tumours and lead to the development of new preventative, diagnostic and therapeutic approaches.

What the reader will gain: We discuss the limitations of our current models and the challenges associated with research into these cancers.

Take home message: The lack of appropriate models for drug development in oesophageal and gastric cancers has hindered the progress of targeted therapy in this field.     

Novel dual Src/Abl inhibitors for hematologic and solid malignancies

Importance of the field: c-Src and Bcr-Abl are two non-receptor or cytoplasmic tyrosine kinases (TKs) that play important roles in the development of solid and hematological malignancies. Indeed, Src is overexpressed or hyperactivated in a variety of solid tumors, while Bcr-Abl is the causative agent of chronic myeloid leukemia (CML), where Src is also involved. The two enzymes share significant sequence homology and remarkable structural resemblance.

Areas covered in this review: ATP-competitive compounds originally developed as Src inhibitors, showed to be also potent Abl inhibitors. Dasatinib, the first dual Src/Abl inhibitor approved by the US FDA in 2006 for the treatment of imatinib-resistant CML, is currently being tested in several clinical trials for the treatment of different solid tumors. SKI-606 and AZD0530 are two other important dual Src/Abl inhibitors extensively tested in animal models and in clinical trials, but not entered into therapy yet.

What the reader will gain: In this review we will report the latest results regarding dasatinib, SKI-606 and AZD0530, but also the knowledge on new compounds that have appeared in the literature in the last few years, including AP24163, AP24534, XL228, DC2036. We will focus on the most recent clinical trials or on preclinical studies that are in progress on these small-molecule TK inhibitors that represent a targeted therapy with high potential against cancer.

Take home message: Molecularly targeted therapies, including the inhibition of specific TKs hyperactivated or overexpressed in many human cancers, could be less toxic than the classical non-specific cytotoxic chemotherapeutic agents; they could offer important therapeutic effects, especially if used in association with other agents such as monoclonal antibodies.     

Induced pluripotent stem cells as cardiac arrhythmic in vitro models and the impact for drug discovery

Introduction: The development of new antiarrhythmic agents is challenging and is hampered by high attrition rate of novel drug candidates. One of the reasons for this is limited predictability of existing preclinical models for drug assessment. Cardiomyocytes (CMs) derived from disease-specific induced pluripotent stem cells (iPSC) represent a novel in vitro cellular model of cardiac arrhythmias with an unprecedented potential for generating new mechanistic insight into disease pathophysiology and improving the process of drug development.

Areas covered: This review outlines recent studies demonstrating the suitability and limitations of iPSC-derived CMs (iPS-CMs) for in vitro modeling inherited arrhythmias and drug testing. The authors focus on channelopathies and outline the properties of iPS-CMs, highlighting their utility and limitations for investigating the mechanism of cardiac arrhythmias and drug discovery.

Expert opinion: The iPS-CMs represent a valuable addition to the already existing armamentarium of cardiac arrhythmic models. However, the superiority of iPS-CMs over other arrhythmia models has not yet been rigorously established and the limitations of the model must be overcome before its full potential for antiarrhythmic drug discovery can be realized. Nevertheless, iPS cell-based platforms hold a great potential for increasing our knowledge about cellular arrhythmia mechanisms and improving the drug discovery process.     

Talaporfin sodium

Importance of the field: Despite therapeutic advances, cancer remains the cause of an estimated 23% of deaths in the USA. New treatments for malignancy are greatly needed.

Areas covered in this review: Talaporfin sodium is a light-activated drug that causes tissue death through induction of apoptosis. Systemic antitumor effects mediated by CD8⁺ T cells have been demonstrated in preclinical studies, providing a mechanism for distant response of tumors noted in clinical trials. Talaporfin sodium is approved in Japan for early-stage endobronchial cancer. Phase I and II studies in solid tumors have shown tumor regression in patients refractory to other therapies. Phase III pivotal studies against hepatocellular carcinoma as monotherapy and liver-metastatic colorectal cancer in combination with chemotherapy are ongoing. Talaporfin sodium is also in studies in men with symptomatic benign prostatic hyperplasia. Substantial safety data from clinical trials so far indicate that the drug is well tolerated.

What the reader will gain: Talaporfin sodium has a broad safety profile and a mode of action that could affect growth in treated and untreated tumors.

Take home message: Clinical and preclinical studies indicate that talaporfin sodium treatment may offer a powerful option to synergize current therapies, as well as an alternative monotherapy in treating cancer.     

The development of acamprosate as a treatment against alcohol relapse

Introduction: Globally, alcohol abuse and dependence are significant contributors to chronic disease and injury and are responsible for nearly 4% of all deaths annually. Acamprosate (Campral), one of only three pharmacological treatments approved for the treatment of alcohol dependence, has shown mixed efficacy in clinical trials in maintaining abstinence of detoxified alcoholics since studies began in the 1980s. Yielding inconsistent results, these studies have prompted skepticism.

Areas covered: Herein, the authors review the preclinical studies which have assessed the efficacy of acamprosate in various animal models of alcohol dependence and discuss the disparate findings from the major clinical trials. Moreover, the authors discuss the major limitations of these preclinical and clinical studies and offer explanations for the often-contradictory findings. The article also looks at the importance of the calcium moiety that accompanies the salt form of acamprosate and its relevance to its activity.

Expert opinion: The recent discovery that large doses of calcium largely duplicate the effects of acamprosate in animal models has introduced a serious challenge to the widely held functional association between this drug and the glutamate neurotransmission system. Future research on acamprosate or newer pharmacotherapeutics should consider assessing plasma and/or brain levels of calcium as a correlate or mediating factor in anti-relapse efficacy. Further, preclinical research on acamprosate has thus far lacked animal models of chemical dependence on alcohol, and the testing of rodents with histories of alcohol intoxication and withdrawal is suggested.     

肿瘤生物模型及其功能性检测的转化潜能和应用

分子靶向治疗和免疫治疗在不同类型的肿瘤中均显示出疗效,已成为肿瘤治疗的新兴领域和方向。二维和三维细胞培养模型、基因工程小鼠模型、类器官模型、患者来源的异种移植瘤（PDX）模型等临床前模型已成为研究肿瘤机制、抗肿瘤药物的研发及预测临床药物疗效的有效工具。然而,肿瘤异质性和微环境的复杂性等在不同程度上影响基于这些临床前模型的功能性检测的真实性和准确性。综述临床前模型的发展情况及功能性检测在药物测试和联合临床试验中的适用性和局限性;为更好地应用于临床,探讨如何将功能性检测利用转化医学的手段使其朝体外诊断（IVD）方向发展,同时分析了目前功能性检测迈向IVD领域所面临的挑战。     

Xenograft and genetically engineered mouse model systems of osteosarcoma and Ewing's sarcoma: tumor models for cancer drug discovery

Introduction: There are > 75 histological types of solid tumors that are classified into two major groups: bone and soft-tissue sarcomas. These diseases are more prevalent in children, and pediatric sarcomas tend to be highly aggressive and rapidly progressive. Sarcomas in adults may follow a more indolent course, but aggressive tumors are also common. Sarcomas that are metastatic at diagnosis, or recurrent following therapy, remain refractory to current treatment options with dismal overall survival rates. A major focus of clinical trials, for patients with sarcoma, is to identify novel and more effective therapeutic strategies targeted to genomic or proteomic aberrations specific to the malignant cells. Critical to the understanding of the potential for targeted therapies are models of disease that are representative of clinical disease and predictive of relevant clinical responses.

Areas covered: In this article, the authors discuss the use of mouse xenograft models and genetically engineered mice in cancer drug discovery. The authors provide a special focus on models for the two most common bone sarcomas: osteosarcoma (OS) and Ewing's sarcoma (ES).

Expert opinion: Predicting whether a new anticancer agent will have a positive therapeutic index in patients with OS and ES remains a challenge. The use of mouse sarcoma models for understanding the mechanisms involved in the response of tumors to new treatments is an important step in the process of drug discovery and the development of clinically relevant therapeutic strategies for these diseases.     

Preclinical safety and efficacy models for pulmonary drug delivery of antimicrobials with focus on in vitro models

New pharmaceutical formulations must be proven as safe and effective before entering clinical trials. Also in the context of pulmonary drug delivery, preclinical models allow testing of novel antimicrobials, reducing risks and costs during their development. Such models allow reducing the complexity of the human lung, but still need to reflect relevant (patho-) physiological features.This review focuses on preclinical pulmonary models, mainly in vitro models, to assess drug safety and efficacy of antimicrobials. Furthermore, approaches to investigate common infectious diseases of the respiratory tract, are emphasized. Pneumonia, tuberculosis and infections occurring due to cystic fibrosis are in focus of this review. We conclude that especially in vitro models offer the chance of an efficient and detailed analysis of new antimicrobials, but also draw attention to the advantages and limitations of such currently available models and critically discuss the necessary steps for their future development.     

Epigenetic approaches for bipolar disorder drug discovery

Introduction: Bipolar disorder (BD) is a common psychiatric disorder which can be devastating to affected patients, if not adequately treated. Although effective drugs are presently available for treating BD, many patients do not respond adequately. There are also problems with the current management of patients with this disorder: drug-resistant BD, rapid-cycling BD and cognitive decline in BD patients despite drug therapy. In this context, new and more effective drugs will be valuable in the clinical management of BD patients.

Areas covered: This article discusses the potential of the use of epigenetic drugs in the management of BD. Although several classes of epigenetic drugs are under investigation, at present, most attention is focused on two classes of epigenetic drugs: DNA methyltransferase inhibitors and histone deacetylase inhibitors (HDACis). Several preclinical drug trials of HDACis for the treatment of BD have been conducted.

Expert opinion: HDACis have shown promising results in preclinical studies of BD. However, the currently available HDACis suffer from acting non-specifically on HDAC isozymes. More isozyme-specific HDACis are likely to have greater efficacy and less toxicity than the current HDACis. It is suggested that efforts should be made to develop such HDACis. Once such HDACis with adequate ability to cross the blood–brain barrier become available, investigators could consider proceeding to clinical trials of HDACis for the treatment of BD.     

Establishing bioequivalence for inhaled drugs; weighing the evidence

Introduction: During drug development and product life-cycle management, it may be necessary to establish bioequivalence between two pharmaceutical products. Methodologies to determine bioequivalence are well established for oral, systemically acting formulations. However, for inhaled drugs, there is currently no universally adopted methodology, and regulatory guidance in this area has been subject to debate.

Areas covered: This paper covers the current status of regulatory guidance on establishing the bioequivalence of topically acting, orally inhaled drugs, the value and limitations of in vitro and in vivo bioequivalence testing, and the practical issues associated with various approaches. The reader will gain an understanding of the issues pertaining to bioequivalence testing of orally inhaled drugs, and the current status of regulatory approaches to establishing bioequivalence in different regions.

Expert opinion: Establishing bioequivalence of inhaled drug products involves a multistep process; however, methodologies for each step have yet to be fully validated. Our lack of understanding about the relationship between in vitro, in vivo and clinical data suggests that in most cases, unless there is a high degree of pharmaceutical equivalence between the test and reference products, consideration of a combination of preclinical and clinical data may be preferable to abridged approaches relying on in vitro data alone.     

Animal models of pancreatic cancer for drug research

Background: The operative and conservative results of therapy in pancreatic ductal adenocarcinoma remain appallingly poor. This underlines the demand for further research for effective anticancer drugs. The various animal models remain the essential method for the determination of efficacy of substances during preclinical phase. Objective: Unfortunately, most of these tested substances showed a good efficacy in pancreatic carcinoma in the animal model but were not confirmed during the clinical phase. Methods: The available literature in PubMed, Medline, Ovid and secondary literature was searched regarding the available animal models for drug testing against pancreatic cancer. The models were analyzed regarding their pros and cons in anticancer drug testing. Conclusion: The different modifications of the orthotopic model (especially in mice) seem at present to be the best model for anticancer testing in pancreatic carcinoma. The value of genetically engineered animal model (GEM) and syngeneic models is on debate. A good selection of the model concerning the questions supposed to be clarified may improve the comparability of the results of animal experiments compared to clinical trials.     

Investigational drugs in early development for treating dengue infection

Introduction: Dengue has emerged as the most significant arboviral disease of the current century. A drug for dengue is an urgent unmet need. As conventional drug discovery efforts have not produced any promising clinical candidates, there is a shift toward re-positioning pre-existing drugs for dengue to fast-track dengue drug development.

Areas covered: This article provides an update on the current status of recently completed and ongoing dengue drug trials. All dengue drug trials described in this article were identified from a list of >230 trials that were returned upon searching the World Health Organization’s International Clinical Trials Registry Platform web portal using the search term ‘dengue’ on December 31^st, 2015.

Expert opinion: None of the handful of drugs tested so far has yielded encouraging results. Early trial experience has served to emphasize the challenge of drug testing in the short therapeutic time window available, the need for tools to predict ‘high-risk’ patients early on and the limitations of the existing pre-clinical model systems. Significant investment of efforts and resources is a must before the availability of a safe, effective and inexpensive dengue drug becomes a reality. Currently, supportive fluid therapy remains the only option available for dengue treatment.