Animal models for modeling pancreatic cancer and novel drug discovery

Introduction: Despite the introduction of novel therapeutic regimens for advanced stages of pancreatic cancer, long-term survival and overall outcome for patients are still very poor. Suitable small animal models are a prerequisite for better understanding of underlying pathophysiology and for translational studies designed to uncover novel therapeutic targets and to evaluate therapy regimens on a preclinical level.

Areas covered: Genetically engineered mouse models as well as syngenic and xenotransplantation models are summarized and critically discussed with respect to their value for pancreatic cancer translational research.

Expert opinion: Mouse models of pancreatic cancer represent a valuable tool for translational studies and are indispensable in order to develop novel potent drugs against pancreatic cancer. More complex genetically engineered mouse models are being developed to cover the complex genomic alterations found in human pancreatic cancers and to enable studies correlating genotype with response to specific therapeutic interventions. Another promising area of research in this field is the refinement and further development of humanized patient-derived xenograft models.     

Preclinical models for pediatric solid tumor drug discovery: current trends,challenges and the scopes for improvement

Introduction: The enhancement in pediatric cancer survival achieved in the past few decades has been confined to low- and moderate-risk cancers, whereas no notable improvement in survival was observed in high-risk and advanced-stage childhood cancers. High attrition rate of candidate drugs in clinical trials is a major hurdle in the development of effective therapies for pediatric solid tumors. In order to reduce the failure rate of candidate drugs in clinical trials, more effective strategies are needed to enhance the predictability of preclinical testing.

Areas covered: The authors have described the current trends in preclinical drug development for treating pediatric solid tumors. Furthermore, the authors review their limitations and the available remedies, with regards to choice of models, pharmacokinetic considerations and the criteria for assessing the long-term efficacy of a candidate drug.

Expert opinion: In many solid tumors, common differences between pediatric and adult cancers have been observed, and therefore, clinical trials for pediatric solid tumors must be conducted on the basis of preclinical observations in pediatric solid tumor models. There is a need to invest in extensive preclinical testing on pediatric solid tumor models. None of the preclinical models can fully recapitulate the human cancers. Therefore, these limitations must be considered while conducting a preclinical trial. The dose and schedule of drugs used for preclinical testing must be clinically relevant. While testing the efficacy of drugs, the markers of apoptosis, drug resistance, hypoxia and tumor-initiating cells can inform us about the long-term therapeutic response of a cancer.     

Novel bone cancer drugs: investigational agents and control paradigms for primary bone sarcomas (Ewing's sarcoma and osteosarcoma)

Background: New investigational agents and chemotherapy regimens including cyclophosphamide + topotecan, temozolomide + irinotecan, and anti-IGF-1R antibodies in Ewing's sarcoma (ES) and liposomal muramyltripeptide phosphatidylethanolamine (L-MTP-PE), aerosol therapy, and bone-specific agents in osteosarcoma (OS) may improve survival and/or quality of life on ‘continuation’ therapy. Objective: Review of investigational approaches and control paradigms for recurrent or metastatic primary bone tumors. Methods: Analyze temozolomide + irinotecan data and review in the context of other newer approaches including antiangiogenesis, anti-IGF-1R antibodies and bisphosphonates for ES. Review some current state-of-the-art approaches for OS including L-MTP-PE, anti-IGF-1R inhibition, aerosol therapies and bone specific agents. Results/conclusion: L-MTP-PE with chemotherapy in OS has been shown to improve survival; compassionate access is available for recurrence and/or metastases. Aerosol therapy (granulocyte–macrophage colony stimulating factor, cisplatin, gemcitabine) for lung metastases is a promising approach to reduce systemic toxicity. The bone-specific agents including denosumab (anti-receptor activator of NF-κB ligand antibody) and bisphosphonates may have benefit against giant cell tumor, ES and OS. Anti-IGF-1R antibody SCH717454 has preclinical activity in OS but best effectiveness will most likely be in combination with chemotherapy earlier in therapy. Both temozolomide + irinotecan and cyclophosphamide + topotecan combinations are very active in ES and are likely to be tested with anti-IGF-1R antibodies against ES.     

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.     

The utility of genetically modified mouse assays for identifying human carcinogens: a basic understanding and path forward. The Alternatives to Carcinogenicity Testing Committee ILSI HESI.

The Alternatives to Carcinogenicity Testing Committee of the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) conducted a large-scale, multinational collaborative research program to evaluate several genetically modified mouse assays for assessing the human carcinogenic potential of compounds. The data from this testing program have made an important contribution to the general understanding of how these models can be best applied in hazard identification; however, questions still exist regarding methodology and data interpretation. To address these issues, ILSI HESI hosted a February 2003 workshop on the Utility of Transgenic Assays for Risk Assessment. The purpose of this workshop was to reach an understanding of how data from genetically modified mouse models are viewed by different regulatory bodies in the pharmaceutical sector and, based on this understanding, to identify areas in which more experimental work may be needed to increase the utility of data derived from these assays. In the course of discussions, various data gaps related to model selection and protocol issues were identified. Based on the outcome of the workshop, various studies are proposed to provide data to improve the utility of currently available assays for cancer hazard identification and risk assessment purposes.     

Blood–brain barrier models and their relevance for a successful development of CNS drug delivery systems: A review

During the research and development of new drugs directed at the central nervous system, there is a considerable attrition rate caused by their hampered access to the brain by the blood–brain barrier. Throughout the years, several in vitro models have been developed in an attempt to mimic critical functionalities of the blood–brain barrier and reliably predict the permeability of drug candidates. However, the current challenge lies in developing a model that retains fundamental blood–brain barrier characteristics and simultaneously remains compatible with the high throughput demands of pharmaceutical industries. This review firstly describes the roles of all elements of the neurovascular unit and their influence on drug brain penetration. In vitro models, including non-cell based and cell-based models, and in vivo models are herein presented, with a particular emphasis on their methodological aspects. Lastly, their contribution to the improvement of brain drug delivery strategies and drug transport across the blood–brain barrier is also discussed.     

Receptor-mediated targeted drug delivery systems for treatment of inflammatory bowel disease: Opportunities and emerging strategies

Inflammatory bowel disease (IBD) is a chronic intestinal disease with painful clinical manifestations and high risks of cancerization. With no curative therapy for IBD at present, the development of effective therapeutics is highly advocated. Drug delivery systems have been extensively studied to transmit therapeutics to inflamed colon sites through the enhanced permeability and retention (EPR) effect caused by the inflammation. However, the drug still could not achieve effective concentration value that merely utilized on EPR effect and display better therapeutic efficacy in the inflamed region because of nontargeted drug release. Substantial researches have shown that some specific receptors and cell adhesion molecules highly expresses on the surface of colonic endothelial and/or immune cells when IBD occurs, ligand-modified drug delivery systems targeting such receptors and cell adhesion molecules can specifically deliver drug into inflamed sites and obtain great curative effects. This review introduces the overexpressed receptors and cell adhesion molecules in inflamed colon sites and retrospects the drug delivery systems functionalized by related ligands. Finally, challenges and future directions in this field are presented to advance the development of the receptor-mediated targeted drug delivery systems for the therapy of IBD.