Not Just a Gut Feeling - GI Foresight
Knowledge of how drugs affect the gastrointestinal (GI) tract is extremely important in the drug development process. It is well documented that adverse drug effects in the GI tract are a factor in novel compound attrition, where studies have shown that 18% of all clinical adverse drug reactions are related to adverse GI effects1.
As well as potentially slowing or inhibiting new drug development programmes, once on the market adverse GI drug effects may impact the quality of life of the patient sufficiently to reduce treatment compliance. This can lead to abandonment of therapy prior to any beneficial outcomes. A wide variety of drugs currently on the market fall into this category from NSAID’s to cholinergic agents, with more than 700 drugs shown to cause diarrohea2. Obviously treatment paradigms would benefit from not having to manage these adverse effects.
So how can we address this issue and improve drug properties?
Profiling in human tissue delivers accurate data on your compound in man, reducing the extent of in vivo animal testing required and eliminating species variation. Early identification of these issues in the drug developmental process would allow compounds that have the potential to cause adverse effects to be recognised and terminated long before they reach the clinical stages, saving resources and time which can be re-distributed to advance more promising drug candidates. Equally, adverse effects seen in preclinical toxicology species may not be representative of the human condition. An understanding of the impact of a compound on the human GI tract prior to clinical trials is valuable for making informed decisions on the progress of a drug development candidate
Biopta’s fresh functional human tissue assays makes this possible by identifying potential adverse effects in human GI tissues. For example.
Effects on GI motility
Gut motility effects are assessed in organ bath experiments using muscle strips, which can be taken from any part of the GI tract. Strips can be stimulated with electrical impulses or drugs and the effects of compound on these responses assessed.
The trace shown in figure 1 is an excellent example of the predictive qualities of Biopta’s fresh human tissue assays. Longitudinal muscle from human colon was mounted in an organ bath and tension measured using a force transducer. Periodic electrical field stimulation (EFS) of the tissue caused enteric nerve stimulation resulting in repeated contractions. Addition of the neurotransmitter 5-hydroxytryptamine (5HT) caused a potentiation of the EFS-induced contraction, in this case by activation of the 5-HT2b receptor, shown to be abundant in the human GI tract especially in the colon longitudinal and circular smooth muscle3. This model system can be used to assess the activity of novel compounds for effects on the contractility of the human gut; causing either a spasm (diarrhoea) or a decrease in the contractile tone (constipation), thus eliminating species variation and providing the closest possible comparison to clinical trials.
Figure 1: Trace depicting a bell shaped curve in response to cumulative concentrations of 5-HT in EFS stimulated colon longitudinal muscle.
Fluid movement assay
Sodium (Na+) and chloride (Cl-) ions play a pivotal role in the regulation of water in the human gut. When an external force such as a novel compound disrupts the balance of these ions away from the physiological norm, it can lead to severe adverse affects i.e. diarrhoea. The trace in figure 2 demonstrates how disruptions to the regular flow of these ions can be demonstrated using Biopta’s fresh human tissue in combination with our Ussing chamber system. The mucosal lining of human gut tissue is dissected free from the smooth muscle layers and mounted across an aperture that separates two temperature-controlled reservoirs containing physiological buffer. Electrical conductivity of the tissue is monitored continuously and the short circuit current (Isc) is used as a measure of overall ion channel activity. The addition of cholera toxin, an agent that is known to induce secretory diarrhoea, to the apical side of the tissue causes an increase in the efflux of Cl- ions via constant activation of the cystic fibrosis transmembrane conductance regulator (CFTR) and this increase in ion efflux is recorded via the Isc. The addition of bumetanide to the basolateral side of the tissue, an inhibitor of the Na-K-Cl transporter, results in a decrease of the Isc.
Figure 2: Trace depicting an increase in the short circuit current (Isc) following the addition of cholera toxin which wasn’t affected by the addition of vehicle but was reduced by the addition of bumetanide.
The assays detailed above demonstrate how adverse GI effects can be screened through the use of Biopta’s fresh human tissue assays. These assays can provide invaluable insight into the potential risks of novel compounds early in their developmental stage which is vital to increasing the supply of new drugs to the market, ideally that have little or no adverse effects.
- Keating, C, et al. 2010. The validation of an in vitro colonic motility assay as a biomarker for gastrointestinal adverse drug reactions. Toxicology and Applied Pharmacology, 245, 299.
- Chassany, O, et al. 2000. Drug-induced diarrhoea. Drug Saf, 22, 53.
- Borman, R, A, et al. 2002. 5-HT2B receptors play a key role in mediating the excitatory effects of 5-HT in human colon in vitro. Br. J. Pharmacol, 135, 1144.