CFTR Mutation: Evaluation of Uptake Kinetics of Ferret Proximal Tubule Cells and Impact of CFTR Modulators on Renal Excretory Profile

Abstract

Pre-clinical testing is an important step in drug development. Generally, in vivo, and in vitro methods are used during pre- clinical stages to test for toxicities and efficacy. In vivo models provide a medium for evaluating pharmacokinetics, pharmacodynamics and margin of safety; however, even with this testing, many drugs may perform well in pre-clinical trials but are discontinued during early phases of clinical trials. This gap is large as many of the drugs developed fall into this category and what may have once looked promising in animal studies and 2D studies do not make it to the patient’s bedside. Microphysiological systems may hold the answer to closing this gap. Microphysiological systems offer unique environments that if validated, can serve to reduce the number of animals used in toxicity studies. These models may be able to identify certain drug properties that are not amenable to be used as therapies earlier in the pre-clinical process. While work has been done to create a ferret kidney on a chip, rats and canines are the most used animal species in the drug development phase. Thus, more work should be done to create a model of rat and canine kidney on a chip utilizing proximal tubule cells that are able to effectively identify species specific toxicities as a result of treatment with drug compounds. We hypothesize that MPS systems will allow for rat proximal tubule cells to maintain normal morphology and will effectively model species -specific nephrotoxicity when exposed to an in vivo relevant toxicant by exhibiting increased kidney injury molecule 1 levels. Of note, antibiotics such as aminoglycosides, polymyxin B and chemotherapeutics are known to carry the risk of nephrotoxicity. Not only is this nephrotoxicity important in seemingly healthy patients, but also patients with diseases such as Cystic Fibrosis who commonly require treatment of complicated infections with high doses of these antibiotics. While there are many models of cystic fibrosis, the ferret model closely resembles a majority of the pathology that human patients face. With alterations in the CFTR gene and increased cubilin shedding in the urine, we hypothesize that kidneys collected from ferrets with a CFTR mutation will have decreased cubilin/megalin complexes at the apical surface of ferret proximal tubule epithelial cells, while the presence of urinary cubilin will be increased at the initial stage of treatment in human CF patients. Renal uptake of proteins and aminoglycosides will be altered due to this phenotype. While some data has been collected in regard to rat proximal tubule cells in 2D culture and MPS as well as evidence of differential uptake of the protein albumin and gentamicin, an amino glycoside, more data is needed to develop a conclusion in both arenas.