The Oncopig Cancer Model as a Complementary Tool for Phenotypic Drug Discovery

The screening of potential therapeutic compounds using phenotypic drug discovery (PDD) is being embraced once again by researchers and pharmaceutical companies as an approach to enhance the development of new effective therapeutics. Before the genomics and molecular biology era and the consecutive emergence of targeted-drug discovery approaches, PDD was the most common platform used for drug discovery. PDD, also known as phenotypic screening, consists of screening potential compounds in either in vitro cellular or in vivo animal models to identify compounds resulting in a desirable phenotypic change. Using this approach, the biological targets of the compounds are not taken into consideration. Suitable animal models are crucial for the continued validation and discovery of new drugs, as compounds displaying promising results in phenotypic in vitro cell-based and in vivo small animal model screenings often fail in clinical trials. Indeed, this is mainly a result of differential anatomy, physiology, metabolism, immunology, and genetics between humans and currently used pre-clinical small animal models. In contrast, pigs are more predictive of therapeutic treatment outcomes in humans than rodents. In addition, pigs provide an ideal platform to study cancer due to their similarities with humans at the anatomical, physiological, metabolic, and genetic levels. Here we provide a mini-review on the reemergence of PDD in drug development, highlighting the potential of porcine cancer models for improving pre-clinical drug discovery and testing. We also present precision medicine based genetically defined swine cancer models developed to date and their potential as biomedical models.

Unraveling the swine genome: implications for human health

The pig was first used in biomedical research in ancient Greece and over the past few decades has quickly grown into an important biomedical research tool. Pigs have genetic and physiological traits similar to humans, which make them one of the most useful and versatile animal models. Owing to these similarities, data generated from porcine models are more likely to lead to viable human treatments than those from murine work. In addition, the similarity in size and physiology to humans allows pigs to be used for many experimental approaches not feasible in mice. Research areas that employ pigs range from neonatal development to translational models for cancer therapy. Increasing numbers of porcine models are being developed since the release of the swine genome sequence, and the development of additional porcine genomic and epigenetic resources will further their use in biomedical research.

Effects of verapamil on the pharmacokinetics and hepatobiliary disposition of fexofenadine in pigs

The pharmacokinetics (PK) of fexofenadine (FEX) in pigs were investigated with the focus on exploring the interplay between hepatic transport and metabolism when administered intravenously (iv) alone or with verapamil. The in vivo pig model enabled simultaneous sampling from plasma (pre-liver, post-liver and peripheral), bile and urine. Each animal was administered FEX 35mg iv alone or with verapamil 35mg. Plasma, bile and urine were analyzed with liquid chromatography-tandem mass spectrometry. Non-compartmental analysis (NCA) was used to estimate traditional PK parameters. In addition, a physiologically based pharmacokinetic (PBPK) model consisting of 11 compartments (6 tissues +5 sample sites) was applied for mechanistic elucidation and estimation of individual PK parameters. FEX had a terminal half-life of 1.7h and a liver extraction of 3%. The fraction of the administered dose of unchanged FEX excreted into the bile was 25% and the bile exposure was more than 100 times higher than the portal vein total plasma exposure, indicating carrier-mediated (CM) disposition processes in the liver. 23% of the administered dose of FEX was excreted unchanged in the urine. An increase in FEX plasma exposure (+50%) and a decrease in renal clearance (-61%) were detected by NCA as a direct effect of concomitant administration of verapamil. However, analysis of the PBPK model also revealed that biliary clearance was significantly inhibited (-53%) by verapamil. In addition, PBPK analysis established that metabolism and CM uptake were important factors in the disposition of FEX in the liver. In conclusion, this study demonstrated that CM transport of FEX in both liver and kidneys was inhibited by a single dose of verapamil.

Investigation of hepatobiliary disposition of doxorubicin following intrahepatic delivery of different dosage forms

Unresectable, intermediate stage hepatocellular carcinoma (HCC) is often treated palliatively in humans by doxorubicin (DOX). The drug is administered either as a drug-emulsified-in-Lipiodol (DLIP) or as drug loaded into drug eluting beads (DEB), and both formulations are administered intrahepatically. However, several aspects of their in vivo performance in the liver are still not well-understood. In this study, DLIP and DEB were investigated regarding the local and systemic pharmacokinetics (PK) of DOX and its primary metabolite doxorubicinol (DOXol). An advanced PK-multisampling site acute in vivo pig model was used for simultaneous sampling in the portal, hepatic, and femoral veins and the bile duct. The study had a randomized, parallel design with four treatment groups (TI-TIV). TI (n = 4) was used as control and received an intravenous (i.v.) infusion of DOX as a solution. TII and TIII were given a local injection in the hepatic artery with DLIP (n = 4) or DEB (n = 4), respectively. TIV (n = 2) received local injections of DLIP in the hepatic artery and bile duct simultaneously. All samples were analyzed for concentrations of DOX and DOXol with UPLC-MS/MS. Compared to DLIP, the systemic exposure for DOX with DEB was reduced (p < 0.05), in agreement with a slower in vivo release. The approximated intracellular bioavailability of DOX during 6 h appeared to be lower for DEB than DLIP. Following i.v. infusion (55 min), DOX had a liver extraction of 41 (28-53)%, and the fraction of the dose eliminated in bile of DOX and DOXol was 20 (15-22)% and 4.2 (3.2-5.2)%, respectively. The AUCbile/AUCVP for DOX and DOXol was 640 (580-660) and 5000 (3900-5400), respectively. In conclusion, DLIP might initially deliver a higher hepatocellular concentration of DOX than DEB as a consequence of its higher in vivo release rate. Thus, DLIP delivery results in higher intracellular peak concentrations that might correlate with better anticancer effects, but also higher systemic drug exposure and safety issues.