Mouse tumour models to guide drug development and identify resistance mechanisms

Genetically Engineered Mouse Models of Liver Tumorigenesis Reveal a Wide Histological Spectrum of Neoplastic and Non-Neoplastic Liver Lesions

Genetically engineered mouse models (GEMM) are an elegant tool to study liver carcinogenesis in vivo. Newly designed mouse models need detailed (histopathological) phenotyping when described for the first time to avoid misinterpretation and misconclusions. Many chemically induced models for hepatocarcinogenesis comprise a huge variety of histologically benign and malignant neoplastic, as well as non-neoplastic, lesions. Such comprehensive categorization data for GEMM are still missing. In this study, 874 microscopically categorized liver lesions from 369 macroscopically detected liver "tumors" from five different GEMM for liver tumorigenesis were included. The histologic spectrum of diagnosis included a wide range of both benign and malignant neoplastic (approx. 82%) and non-neoplastic (approx. 18%) lesions including hyperplasia, reactive bile duct changes or oval cell proliferations with huge variations among the various models and genetic backgrounds. Our study therefore critically demonstrates that models of liver tumorigenesis can harbor a huge variety of histopathologically distinct diagnosis and, depending on the genotype, notable variations are expectable. These findings are extremely important to warrant the correct application of GEMM in liver cancer research and clearly emphasize the role of basic histopathology as still being a crucial tool in modern biomedical research.

The Mouse Hospital and Its Integration in Ultra-Precision Approaches to Cancer Care

Precision medicine holds real promise for the treatment of cancer. Adapting therapeutic strategies so patients receive individualized treatment protocols, will transform how diseases like cancer are managed. Already, molecular profiling technologies have provided unprecedented capacity to characterize tumors, yet the ability to translate this to actionable outcome in the clinic is limited. To enable real time translation of personalized therapeutic approaches to patient care in a co-clinical manner will require the adoption and integration of approaches that facilitate modeling of patient disease. The Mouse Hospital represents an approach that is ideally suited to pre- and co-clinical evaluation of novel therapeutic strategies for clinical care. Patient derived xenograft (PDX) technologies and in situ tumor modeling approaches using genetically engineered mouse models (GEMMs) already have a proven capacity to mimic human tumor responses, and their application can deliver invaluable insights into appropriate clinical approaches for individual patients by mirroring human clinical trials using a Co-Clinical Trial project and Mouse Hospital infrastructure. Additionally, the integration of the Mouse Hospital with other emerging technologies for the application of precision medicines, including organoid technologies, provides a platform that enables medical centers to truly reap the benefits that precision medicine has to offer.

Doxorubicin-provoked increase of mitotic activity and concomitant drain of G0-pool in therapy-resistant BE(2)-C neuroblastoma

In this study chemotherapy response in neuroblastoma (NB) was assessed for the first time in a transplantation model comprising non-malignant human embryonic microenvironment of pluripotent stem cell teratoma (PSCT) derived from diploid bona fide hESC. Two NB cell lines with known high-risk phenotypes; the multi-resistant BE(2)-C and the drug sensitive IMR-32, were transplanted to the PSCT model and the tumour growth was exposed to single or repeated treatments with doxorubicin, and thereafter evaluated for cell death, apoptosis, and proliferation. Dose dependent cytotoxic effects were observed, this way corroborating the experimental platform for this type of analysis. Notably, analysis of doxorubicin-resilient BE(2)-C growth in the PSCT model revealed an unexpected 1,5-fold increase in Ki67-index (p<0.05), indicating that non-cycling (G0) cells entered the cell cycle following the doxorubicin exposure. Support for this notion was obtained also in vitro. A pharmacologically relevant dose (1μM) resulted in a marked accumulation of Ki67 positive BE(2)-C cells (p<0.0001), as well as a >3-fold increase in active cell cycle (i.e. cells positive staining for PH3 together with incorporation of EdU) (p<0.01). Considering the clinical challenge for treating high-risk NB, the discovery of a therapy-provoked growth-stimulating effect in the multi-resistant and p53-mutated BE(2)-C cell line, but not in the drug-sensitive p53wt IMR-32 cell line, warrants further studies concerning generality and clinical significance of this new observation.

New Mechanisms of Resistance to MEK Inhibitors in Melanoma Revealed by Intravital Imaging

Targeted therapeutics that are initially effective in cancer patients nearly invariably engender resistance at some stage, an inherent challenge in the use of any molecular-targeted drug in cancer settings. In this study, we evaluated resistance mechanisms arising in metastatic melanoma to MAPK pathway kinase inhibitors as a strategy to identify candidate strategies to limit risks of resistance. To investigate longitudinal responses, we developed an intravital serial imaging approach that can directly visualize drug response in an inducible RAF-driven, autochthonous murine model of melanoma incorporating a fluorescent reporter allele (tdTomatoLSL). Using this system, we visualized formation and progression of tumors in situ, starting from the single-cell level longitudinally over time. Reliable reporting of the status of primary murine tumors treated with the selective MEK1/2 inhibitor (MEKi) trametinib illustrated a time-course of initial drug response and persistence, followed by the development of drug resistance. We found that tumor cells adjacent to bundled collagen had a preferential persistence in response to MEKi. Unbiased transcriptional and kinome reprogramming analyses from selected treatment time points suggested increased c-Kit and PI3K/AKT pathway activation in resistant tumors, along with enhanced expression of epithelial genes and epithelial-mesenchymal transition downregulation signatures with development of MEKi resistance. Similar trends were observed following simultaneous treatment with BRAF and MEK inhibitors aligned to standard-of-care combination therapy, suggesting these reprogramming events were not specific to MEKi alone. Overall, our results illuminate the integration of tumor-stroma dynamics with tissue plasticity in melanoma progression and provide new insights into the basis for drug response, persistence, and resistance.Significance: A longitudinal study tracks the course of MEKi treatment in an autochthonous imageable murine model of melanoma from initial response to therapeutic resistance, offering new insights into the basis for drug response, persistence, and resistance. Cancer Res; 78(2); 542-57. ©2017 AACR.

The fourth annual BRDS on genome editing and silencing for precision medicines

Precision medicine is promising for treating human diseases, as it focuses on tailoring drugs to a patient's genes, environment, and lifestyle. The need for personalized medicines has opened the doors for turning nucleic acids into therapeutics. Although gene therapy has the potential to treat and cure genetic and acquired diseases, it needs to overcome certain obstacles before creating the overall prescription drugs. Recent advancement in the life science has helped to understand the effective manipulation and delivery of genome-engineering tools better. The use of sequence-specific nucleases allows genetic changes in human cells to be easily made with higher efficiency and precision than before. Nanotechnology has made rapid advancement in the field of drug delivery, but the delivery of nucleic acids presents unique challenges. Also, designing efficient and short time-consuming genome-editing tools with negligible off-target effects are in high demand for precision medicine. In the fourth annual Biopharmaceutical Research and Development Symposium (BRDS) held at the University of Nebraska Medical Center (UNMC) on September 7-8, 2017, we covered different facets of developing tools for precision medicine for therapeutic and diagnosis of genetic disorders.

The Challenges of Modeling Drug Resistance to Antiangiogenic Therapy

Drug resistance remains an ongoing challenge for the majority of patients treated with inhibitors of the vascular endothelial growth factor (VEGF) pathway, a key regulator of tumor angiogenesis. Preclinical models have played a significant role in identifying multiple complex mechanisms of antiangiogenic treatment failure. Yet questions remain about the optimal methodology to study resistance that may assist in making clinically relevant choices about alternative or combination treatment strategies. The origins of antiangiogenic treatment failure may stem from the tumor vasculature, the tumor itself, or both together, and preclinical methods that define resistance are diverse and rarely compared. We performed a literature search of the preclinical methodologies used to examine resistance to VEGF pathway inhibitors and identified 109 papers from more than 400 that use treatment failure as the starting point for mechanistic study. We found that definitions of resistance are broad and inconsistent, involve only a small number of reagents, and derive mostly from in vitro and in vivo methodologies that often do not represent clinically relevant disease stages or progression. Together, this literature analysis highlights the challenges of studying inhibitors of the tumor microenvironment in the preclinical setting and the need for improved methodology to assist in qualifying (and quantifying) treatment failure to identify mechanisms that will help predict alternative strategies in patients.

Modeling of Patient-Derived Xenografts in Colorectal Cancer

Developing realistic preclinical models using clinical samples that mirror complex tumor biology and behavior are vital to advancing cancer research. While cell line cultures have been helpful in generating preclinical data, the genetic divergence between these and corresponding primary tumors has limited clinical translation. Conversely, patient-derived xenografts (PDX) in colorectal cancer are highly representative of the genetic and phenotypic heterogeneity in the original tumor. Coupled with high-throughput analyses and bioinformatics, these PDXs represent robust preclinical tools for biomarkers, therapeutic target, and drug discovery. Successful PDX engraftment is hypothesized to be related to a series of anecdotal variables namely, tissue source, cancer stage, tumor grade, acquisition strategy, time to implantation, exposure to prior systemic therapy, and genomic heterogeneity of tumors. Although these factors at large can influence practices and patterns related to xenotransplantation, their relative significance in determining the success of establishing PDXs is uncertain. Accordingly, we systematically examined the predictive ability of these factors in establishing PDXs using 90 colorectal cancer patient specimens that were subcutaneously implanted into immunodeficient mice. Fifty (56%) PDXs were successfully established. Multivariate analyses showed tissue acquisition strategy [surgery 72.0% (95% confidence interval (CI): 58.2-82.6) vs. biopsy 35% (95% CI: 22.1%-50.6%)] to be the key determinant for successful PDX engraftment. These findings contrast with current empiricism in generating PDXs and can serve to simplify or liberalize PDX modeling protocols. Better understanding the relative impact of these factors on efficiency of PDX formation will allow for pervasive integration of these models in care of colorectal cancer patients. Mol Cancer Ther; 16(7); 1435-42. ©2017 AACR.

Preclinical evaluation of taxane-binding peptide-modified polymeric micelles loaded with docetaxel in an orthotopic breast cancer mouse model

We developed a novel taxane-binding peptide (TBP) modified, biodegradable polymeric micelle that overcomes limitations of drug loading and poor serum stability typically seen with particle delivery, leading to enhanced pharmacokinetics and tumor distribution of docetaxel (DTX). The use of the taxane-binding peptide to increase docetaxel loading is particularly compelling as it takes advantage of a known intracellular binding mechanism in a new way. Docetaxel is a potent chemotherapeutic with a therapeutic index often limited by the toxicity of the excipients that are necessary to enhance its solubility for intravenous delivery. Our polymeric micelle has terminal furan groups that enable facile antibody Fab conjugation by Diels-Alder chemistry for targeted delivery. Compared to the conventional ethanolic polysorbate 80 formulation (Free DTX), our nanoparticle (NP DTX) formulation exhibited a two-fold increase in exposure and tumor accumulation. Notably, the reduced toxicity of the NP DTX formulation increased the therapeutic index and allowed for higher dosing regimens, with a maximum tolerated dose (MTD) 1.6-fold higher than that of the Free DTX formulation, which is significant and similar to enhancements observed in clinical products for docetaxel and other drugs. These improved properties led to enhanced mouse survival in an orthotopic model of breast cancer; however, the targeted formulation of Fab-NP DTX did not further improve efficacy. Together, these results clearly demonstrate the benefits of the TBP-modified polymeric micelles as promising carriers for docetaxel.

Quantitation of Murine Stroma and Selective Purification of the Human Tumor Component of Patient-Derived Xenografts for Genomic Analysis

Patient-derived xenograft (PDX) mouse models are increasingly used for preclinical therapeutic testing of human cancer. A limitation in molecular and genetic characterization of PDX tumors is the presence of integral murine stroma. This is particularly problematic for genomic sequencing of PDX models. Rapid and dependable approaches for quantitating stromal content and purifying the malignant human component of these tumors are needed. We used a recently developed technique exploiting species-specific polymerase chain reaction (PCR) amplicon length (ssPAL) differences to define the fractional composition of murine and human DNA, which was proportional to the fractional composition of cells in a series of lung cancer PDX lines. We compared four methods of human cancer cell isolation: fluorescence-activated cell sorting (FACS), an immunomagnetic mouse cell depletion (MCD) approach, and two distinct EpCAM-based immunomagnetic positive selection methods. We further analyzed DNA extracted from the resulting enriched human cancer cells by targeted sequencing using a clinically validated multi-gene panel. Stromal content varied widely among tumors of similar histology, but appeared stable over multiple serial tumor passages of an individual model. FACS and MCD were superior to either positive selection approach, especially in cases of high stromal content, and consistently allowed high quality human-specific genomic profiling. ssPAL is a dependable approach to quantitation of murine stromal content, and MCD is a simple, efficient, and high yield approach to human cancer cell isolation for genomic analysis of PDX tumors.

The Development of a Recombinant scFv Monoclonal Antibody Targeting Canine CD20 for Use in Comparative Medicine

Monoclonal antibodies are leading agents for therapeutic treatment of human diseases, but are limited in use by the paucity of clinically relevant models for validation. Sporadic canine tumours mimic the features of some human equivalents. Developing canine immunotherapeutics can be an approach for modeling human disease responses. Rituximab is a pioneering agent used to treat human hematological malignancies. Biologic mimics that target canine CD20 are just being developed by the biotechnology industry. Towards a comparative canine-human model system, we have developed a novel anti-CD20 monoclonal antibody (NCD1.2) that binds both human and canine CD20. NCD1.2 has a sub-nanomolar K_d as defined by an octet red binding assay. Using FACS, NCD1.2 binds to clinically derived canine cells including B-cells in peripheral blood and in different histotypes of B-cell lymphoma. Immunohistochemical staining of canine tissues indicates that the NCD1.2 binds to membrane localized cells in Diffuse Large B-cell lymphoma, Marginal Zone Lymphoma, and other canine B-cell lymphomas. We cloned the heavy and light chains of NCD1.2 from hybridomas to determine whether active scaffolds can be acquired as future biologics tools. The V_H and V_L genes from the hybridomas were cloned using degenerate primers and packaged as single chains (scFv) into a phage-display library. Surprisingly, we identified two scFv (scFv-3 and scFv-7) isolated from the hybridoma with bioactivity towards CD20. The two scFv had identical V_H genes but different V_L genes and identical CDR3s, indicating that at least two light chain mRNAs are encoded by NCD1.2 hybridoma cells. Both scFv-3 and scFv-7 were cloned into mammalian vectors for secretion in CHO cells and the antibodies were bioactive towards recombinant CD20 protein or peptide. The scFv-3 and scFv-7 were cloned into an ADEPT-CPG2 bioconjugate vector where bioactivity was retained when expressed in bacterial systems. These data identify a recombinant anti-CD20 scFv that might form a useful tool for evaluation in bioconjugate-directed anti-CD20 immunotherapies in comparative medicine.

Drug discovery in ophthalmology: past success, present challenges, and future opportunities

BACKGROUND

Drug discovery has undergone major transformations in the last century, progressing from the recognition and refinement of natural products with therapeutic benefit, to the systematic screening of molecular libraries on whole organisms or cell lines and more recently to a more target-based approach driven by greater knowledge of the physiological and pathological pathways involved. Despite this evolution increasing challenges within the drug discovery industry are causing escalating rates of failure of development pipelines.

DISCUSSION

We review the challenges facing the drug discovery industry, and discuss what attempts are being made to increase the productivity of drug development, including a refocusing on the study of the basic biology of the disease, and an embracing of the concept of 'translational research'. We consider what ophthalmic drug discovery can learn from the sector in general and discuss strategies to overcome the present limitations. This includes advances in the understanding of the pathogenesis of disease; improvements in animal models of human disease; improvements in ophthalmic drug delivery and attempts at patient stratification within clinical trials. As we look to the future, we argue that investment in ophthalmic drug development must continue to cover the whole translational spectrum (from 'bench to bedside and back again') with recognition that both biological discovery and clinical understanding will drive drug discovery, providing safe and effective therapies for ocular disease.

Studying platinum sensitivity and resistance in high-grade serous ovarian cancer: Different models for different questions

High-grade serous ovarian cancer (HGSOC) has the highest mortality rate among all gynecological cancers. Patients are generally diagnosed in an advanced stage with the majority of cases displaying platinum resistant relapses. Recent genomic interrogation of large numbers of HGSOC patient samples indicated high complexity in terms of genetic aberrations, intra- and intertumor heterogeneity and underscored their lack of targetable oncogenic mutations. Sub-classifications of HGSOC based on expression profiles, termed 'differentiated', 'immunoreactive', 'mesenchymal' and 'proliferative', were shown to have prognostic value. In addition, in almost half of all HGSOC patients, a deficiency in homologous recombination (HR) was found that potentially can be targeted using PARP inhibitors. Developing precision medicine requires advanced experimental models. In the current review, we discuss experimental HGSOC models in which resistance to platinum therapy and the use of novel therapeutics can be carefully studied. Panels of better-defined primary cell lines need to be established to capture the full spectrum of HGSOC subtypes. Further refinement of cell lines is obtained with a 3-dimensional culture model mimicking the tumor microenvironment. Alternatively, ex vivo ovarian tumor tissue slices are used. For in vivo studies, larger panels of ovarian cancer patient-derived xenografts (PDXs) are being established, encompassing all expression subtypes. Ovarian cancer PDXs grossly retain tumor heterogeneity and clinical response to platinum therapy is preserved. PDXs are currently used in drug screens and as avatars for patient response. The role of the immune system in tumor responses can be assessed using humanized PDXs and immunocompetent genetically engineered mouse models. Dynamic tracking of genetic alterations in PDXs as well as patients during treatment and after relapse is feasible by sequencing circulating cell-free tumor DNA and analyzing circulating tumor cells. We discuss how various models and methods can be combined to delineate the molecular mechanisms underlying platinum resistance and to select HGSOC patients other than BRCA1/2-mutation carriers that could potentially benefit from the synthetic lethality of PARP inhibitors. This integrated approach is a first step to improve therapy outcomes in specific subgroups of HGSOC patients.

CRISPR-Cas9: A Revolutionary Tool for Cancer Modelling

The cancer-modelling field is now experiencing a conversion with the recent emergence of the RNA-programmable CRISPR-Cas9 system, a flexible methodology to produce essentially any desired modification in the genome. Cancer is a multistep process that involves many genetic mutations and other genome rearrangements. Despite their importance, it is difficult to recapitulate the degree of genetic complexity found in patient tumors. The CRISPR-Cas9 system for genome editing has been proven as a robust technology that makes it possible to generate cellular and animal models that recapitulate those cooperative alterations rapidly and at low cost. In this review, we will discuss the innovative applications of the CRISPR-Cas9 system to generate new models, providing a new way to interrogate the development and progression of cancers.

The challenges facing block copolymer micelles for cancer therapy: In vivo barriers and clinical translation

The application of block copolymer micelles (BCMs) in oncology has benefitted from advances in polymer chemistry, drug formulation and delivery as well as in vitro and in vivo biological models. While great strides have been made in each of these individual areas, there remains some disappointment overall, citing, in particular, the absence of more BCM formulations in clinical evaluation and practice. In this review, we aim to provide an overview of the challenges presented by in vivo systems to the effective design and development of BCMs. In particular, the barriers posed by systemic administration and tumor properties are examined. The impact of critical features, such as the size, stability and functionalization of BCMs is discussed, while key pre-clinical endpoints and models are critiqued. Given clinical considerations, we present this work as a means to stimulate a renewed focus on the unique chemical versatility bestowed by BCMs and a measured grasp of representative in vitro and in vivo models.

Prodding the Beast: Assessing the Impact of Treatment-Induced Metastasis

The arsenal of treatments for most cancers fit broadly into the categories of surgery, chemotherapy, radiation, and targeted therapy. All represent proven and successful strategies, yet each can trigger local (tumor) and systemic (host) processes that elicit unwanted, often opposing, influences on cancer growth. Under certain conditions, nearly all cancer treatments can facilitate metastatic spread, often in parallel (and sometimes in clear contrast) with tumor reducing benefits. The paradox of treatment-induced metastasis (TIM) is not new. Supporting preclinical studies span decades, but are often overlooked. With recent evidence of prometastatic effects following treatment with targeted agents blocking the tumor microenvironment, a closer inspection of this literature is warranted. The TIM phenomena may diminish the impact of effective therapies and play a critical role in eventual resistance. Alternatively, it may simply exemplify the gap between animal and human studies, and therefore have little impact for patient disease and treatment. This review will focus on the preclinical model systems used to evaluate TIM and explore the mechanisms that influence overall treatment efficacy. Understanding the role of TIM in established and emerging drug treatment strategies may help provide rationales for future drug combination approaches with antimetastatic agents to improve outcomes and reduce resistance.

Impact of the spheroid model complexity on drug response

Pharmaceutical investigators are searching for preclinical models closely resembling the original cancer and predicting clinical outcome. This study compares drug response of three in vitro 3D-drug screening models with different complexity. Tumor cell line spheroids were generated from the cell lines Caco-2, DLD-1, COLO 205, HT-29 and HCT-116, and treated with clinically relevant combination therapies, namely 5-FU/oxaliplatin (FO), 5-FU/irinotecan (FI) and the molecular drugs Cetuximab, Trastuzumab, Vorinostat and Everolimus. Treatment results were compared with spheroids originated from tumor cell lines (Caco-2, DLD-1) co-cultured with stromal cells (PBMCs, cancer-associated fibroblasts of colorectal origin) and spheroids directly prepared from colon cancer tissues. Different microenvironment compositions altered the tumor cell line spheroid response patterns. Adding PBMCs increased resistance to FO treatment by 10-15% in Caco-2 and DLD-1 spheroids but decreased resistance to FI by 16% in DLD-1 spheroids. Fibroblast co-cultures decreased resistance to FI in Caco-2 spheroids by 38% but had no impact on FO. Treatment of colon cancer tissue spheroids revealed three distinct response pattern subgroups not detectable in 3D cell lines models. The cancer tissue spheroid model mimics both tumor characteristics and the stromal microenvironment and therefore is an invaluable screening model for pharmaceutical drug development.

Progress towards personalized medicine for ameloblastoma

Ameloblastoma is a locally infiltrative benign odontogenic neoplasm. Tumours may be large, destructive and recurrent, requiring radical surgery with associated facial deformity and morbidity. The molecular pathogenesis of this tumour has been unclear, retarding the development of non-invasive gene-targeted therapies. In a recent paper in this journal, Kurppa et al. [4] showed that EGFR-targeted therapy blocked cell proliferation in an ameloblastoma primary cell culture. That this therapy was not effective in another primary cell culture led to the discovery of the oncogenic BRAF V600E mutation in a high proportion (63%) of ameloblastoma samples. By defining two separate pathways, both of which can be specifically targeted, these findings are an important step towards personalized medicine of ameloblastoma. We discuss the findings in the broader context of ameloblastoma, as well as the effects of tumour microenvironment and molecular heterogeneity that need to be taken into account when considering the use of personalized therapies based on specific genetic mutations in individual patients.

Pathology in drug discovery and development

The rapid pace of drug discovery and drug development in oncology, immunology and ophthalmology brings new challenges; the efficient and effective development of new targeted drugs will require more detailed molecular classifications of histologically homogeneous diseases that show heterogeneous clinical outcomes. To this end, single companion diagnostics for specific drugs will be replaced by multiplex diagnostics for entire therapeutic areas, preserving tissue and enabling rapid molecular taxonomy. The field will move away from the development of new molecular entities as single agents, to which resistance is common. Instead, a detailed understanding of the pathological mechanisms of resistance, in patients and in preclinical models, will be key to the validation of scientifically rational and clinically effective drug combinations. To remain at the heart of disease diagnosis and appropriate management, pathologists must evolve into translational biologists and biomarker scientists. Herein, we provide examples of where this metamorphosis has already taken place, in lung cancer and melanoma, where the transformation has yet to begin, in the use of immunotherapies for ophthalmology and oncology, and where there is fertile soil for a revolution in treatment, in efforts to classify glioblastoma and personalize treatment. The challenges of disease heterogeneity, the regulatory environment and adequate tissue are ever present, but these too are being overcome in dedicated academic centres. In summary, the tools necessary to overcome the 'whens' and 'ifs' of the molecular revolution are in the hands of pathologists today; it is a matter of standardization, training and leadership to bring these into routine practice and translate science into patient benefit. This Annual Review Issue of the Journal of Pathology highlights the central role for pathology in modern drug discovery and development.