For decades, drug discovery has relied on immortalized cell lines and animal models to investigate signalling pathways, gene expression, disease mechanisms, protein synthesis, drug safety, efficiency and ultimately predict clinical utility. Yet there is intrinsic problems and limitations besetting preclinical research which often, inevitably, creates a radical disconnect between preclinical and clinical domains. As described by Kraniklidis (2012) cancer cell lines, for example, suffer from bad "cell genealogy" with tumour metastases (eg. ZR75.1) ot pleural effusions (infamous Michigan Cancer Foundation MCF-7 line, ER-negative MDA-MB-231, Sloan-Ketterings SkBr3 HER2-active) being used to study primary breast tumours, which as shown by mass spectrometry analysis have clear differences in proteomic profile (eg. T47D and MCF-7 have a contrast in the expression of 164 proteins, involved in growth stimulation, anti-apoptosis mechanisms, transcription repression). There is another issue in the literature with regards to the issue of metastatic transformation - i.e. human clinical levels ER+ tumours frequently invade locally and metastasize (bone, etc) in patients, yet tumours in mice are poorly invasive. And the list continues.
Human Induced Pluripotent Stem Cell technology (hiPSC, first described in 2007) can be differentiated into many cell types - neurons, cardiomycocytes, neural crest cells and hematopoietic cells - and have a comparable level of pluripotency as human embryonic stem cells (hESCs) [without the ethical restrictions from using fertlized human embryos]. These research tools are now allowing investigation into a wide range of disorders, including rare diseases, those with multi-factorial origin (genetic or environmental) and conditions that manifest later in life such as Alzheimers Dementia, Huntington chorea and Parkinson's disease. The entire genomic background of a patient can be retained and that is integral for clinical modelling - schizophrenia for example is not a cause of a single genetic mutation. hiPSC-derived cells show many of the characteristics implicated in the clinical phenotype and As the "Concise Review: Drug Discovery in the Age of the iPSC" detailed the incorporation of this technology will allow a "more powerful and nuanced approach to personalized medicine".
So what 'mini-organs' are being developed in preclinical research? Here is five examples:
March 2015 has been a prolific month for developments in this technology. A few days ago a team from the University of Cambridge created "mini-lungs" using stem cells derived from the skins of cystic fibrosis patients (CFTR-expressing airway epithelial cells) giving a new protocol for drug discovery, tissue regeneration and disease modelling. This was preceded by a Stem Cells Development paper describing how researchers had overcome the use of non-CNS (central nervous system) immortalized cell lines to engineer a personalized model of disease, "bringing toxicology into the 21st century".
Certainly by bringing novel technologies such as this to the fore, it is clear there is a paradigm shift towards greater development of diversity panels, genomic engineering tools and modified high content screens - either via patient specific or isogenic lines differentiating into several neural cell types for detailed comparison. Finally bioengineers from UC Berkeley presented a network of pulsating cardiac muscle cells housed in an inch-long silicone device, a model system for drug-screening in cardiovascular medications. The report in Scientific Reports and funded by the Tissue Chip for Drug Screening Initiative (launched by the NIH) described a 3D structure that would be comparable to the geometry and spacing of connective tissue fiber in a human heart. Microfluidic channels on either side of the cell area served as models blood vessels, mimicking the diffusion of nutrients and drugs into the cardiac tissue. When tested as a predictable model, the scientists increased a baseline beats rate state of 55-80 to 124 using Bradycadia (a drug used to treat slow heart rate). Now, following this success, the lab wants to produce a multi-organ system.
"Linking heart and liver tissue would allow us to determine whether a drug that initially works well in the heart might later be metabolized by the liver in a way that would be toxic" - Research leader, Prof Kevin Healy.