Biomimetic Urothelial Tissue Models for the in Vitro Evaluation of Barrier Physiology and Bladder Drug Efficacy

Abstract

The bladder is an important tissue in which to evaluate xenobiotic drug interactions and toxicities due to the concentration of parent drug and hepatic/enteric-derived metabolites in the urine as a result of renal excretion. Breaching of the barrier provided by the bladder epithelial lining (the urothelium) can expose the underlying tissues to urine and cause harmful effects (e.g., cystitis or cancer). Human urothelium is most commonly represented in vitro as immortalized or established cancer-derived cell lines, but the compromised ability of such cells to undergo differentiation and barrier formation means that nonimmortalized, normal human urothelial (NHU) cells provide a more relevant cell culture system. The impressive capacity for urothelial self-renewal in vivo can be harnessed in vitro to generate experimentally-useful quantities of NHU cells, which can subsequently be differentiated to form a functional or "biomimetic" urothelium. When seeded onto permeable membranes, these barrier-forming human urothelial tissue models enable the modeling of serum and luminal (intravesical) exposure to drugs and metabolites, thus supporting efficacy/toxicity assessments. Biomimetic human urothelial constructs provide a potential step along the preclinical trail and may support the extrapolation from rodent in vivo data to determine human relevance. Early evidence is beginning to demonstrate that human urothelium in vitro can provide information that supersedes conventional rodent studies, but further validation is needed to support widespread adoption.

Differentiation‐associated urothelial cytochrome P450 oxidoreductase predicates the xenobiotic‐metabolizing activity of “luminal” muscle‐invasive bladder cancers

“…The aim of this study was to establish the potential of bladder CYP1 metabolism; using in vitro cell culture models representing normal and neoplastic human urothelium in undifferentiated and differentiated states (reviewed in Ref. ). Immunohistology was used to relate in vitro findings to the biology of human bladder tissue and muscle‐invasive bladder cancers (MIBC).…”

“…The aim of this study was to establish the potential of bladder CYP1 metabolism; using in vitro cell culture models representing normal and neoplastic human urothelium in undifferentiated and differentiated states (reviewed in Ref. 20 21 For the studies described here, 15 independent cell lines were used between passages one and five. In the figures, each independent donor NHU cell line used has been given a unique symbol consistent between every panel (including supplementary).…”

A urine-dependent human urothelial organoid offers a promising alternative to rodent models of infection

“…In addition to the uroplakin family, the urothelium also elaborates a mucopolysaccharide-rich layer of glycosaminoglycans (GAG) which is believed to protect the bladder from infection and urine-born irritants 22 , of which chondroitin sulphate, heparan sulphate, hyaluronic acid, dermatan sulphate and keratin sulphate are the most studie 23 . Chondroitin sulphate, in particular, is believed to play a key role in urothelial barrier function and exhibits luminal and basal expression in both human and porcine bladders 24 .…”

“…A number of promising 3D urothelial models have been described in the literature, the majority of which have been discussed in a comprehensive review by Baker et al (2014) 22 .…”

“…Briefly, existing bladder models are produced using one of three broad culture techniques: (1) organ culture of intact biopsies or explant culture; (2) culture of urothelial cells naturally shed into the urine or harvested from biopsies; and (3) organotypic culture whereby normal urothelial cells are stimulated to form 3D organoids on filter inserts 22 . Although arguably the most relevant model system, organ culture of intact human tissue is time consuming, yields a finite amount of experimental material and requires fresh human tissue 22,40 . Due to these limitations, a number of researchers have used rodent bladder biopsies.…”