Title:Reactive Metabolites in Early Drug Development: Predictive In vitro Tools
Volume: 22
Issue: 4
Author(s): Olavi Pelkonen, Markku Pasanen, Ari Tolonen, Mikko Koskinen, Jukka Hakkola, Khaled Abass, Jaana Laine, Merja Hakkinen, Risto Juvonen, Seppo Auriola, Markus Storvik, Pasi Huuskonen, Timo Rousu and Maiju Rahikkala
Affiliation:
Keywords:
CYP, cytochrome P450, drug metabolizing enzymes, glutathione, oligonucleotide trappers, oligopeptide trappers,
potassium cyanide, reactive metabolites, semicarbazide, trapping agents.
Abstract: Drug metabolism can result in the formation of highly reactive metabolites that are known to play a role in toxicity
resulting in a significant proportion of attrition during drug development and clinical use. Thus, the earlier such reactivity
was detected, the better. This review summarizes our multi-year project, together with pertinent literature, to examine
a battery of in vitro tests capable of detecting the formation of reactive metabolites. Principal prerequisites for such
tests were delineated: chemicals known/not known to cause tissue injury and produce reactive metabolites, activation system
(mainly human-derived), small- and large-molecular targets (small-molecular trappers, peptides, proteins), analytical
techniques (mass spectrometry), and cellular toxicity biomarkers. The current status of in vitro tools to detect reactive intermediates
is the following: 1. Small-molecular trapping agents such glutathione or cyanide detect the production of reactive
species with high sensitivity by proper MS technique. However, it seems that also putative “negatives” give rise to
corresponding adducts. 2. Results from peptide and dG (DNA targeting) trapper studies are generally in line with those of
small-molecular trappers, although also important differences exist. These two trapping platforms do not overlap. 3. It is
anticipated that the in vitro adduct studies could be fully interpreted only in conjunction with toxicity biomarker (such as
the Nrf2 pathway) information from whole cells or tissues. However, while there are tools to characterize the chemical liability
and there are correlation between individual/integrated endpoints and toxicity, there are still severe gaps in understanding
the mechanisms behind the link between reactive metabolites and adverse effects.
