EXPERIMENTAL APPROACHES TO THE STUDY OF DRUG TRANSPORTERS - Drug Transporters: Molecular Characterization and Role in Drug Disposition - page 551

18.7. CONCLUSIONS
In this chapter we have presented methodological aspects of popular approaches to
the study of drug transporters. Application of these methods to study pharmacologi-
cal issues is considered in detail in other chapters. We have focused on methods that
we have employed ourselves, because descriptions based on actual examples should
be easier to understand. In the case of transport studies, we have described exper-
iments with radiolabeled probe compounds, but HPLC or LC/MS/MS systems are
also suitable for this purpose.
As mentioned in our introduction, it is important for research in this field to apply
state-of-the-art technology, so finally, we introduce some novel approaches for the
study of transporters (Figure 18.2). Saitoh and others used a baculoviral expression
system to obtain a large amount of purified PEPT1. This technology is likely to become
a useful one to study the functions, activities, regulation, and crystal structures of drug
transporters. 66 - 68 In vivo imaging systems such as positron emission tomography
(PET) and computed tomography (CT) are used widely in clinical diagnostics and
can be modified for use with small animals such as rodents. They can be used to
visualize cellular and molecular events, in drug-treated living animals, and can be
powerful tools for in vivo experiments under physiological conditions. 69 , 70 Single-
nucleotide polymorphism (SNP) analyses with clinical samples can help to elucidate
the physiological and pharmacological functions or importance of drug transporters.
Recently, the involvement of transporters in drug-drug interaction has been reported,
based on examination of SNPs and clinical samples. Understanding the SNPs of
transporters and associated proteins may contribute to the establishment of “tailor-
made medicine.” 71 - 75
Many methods are available for similar purposes, and the choice of methods may
depend on the research environments, such as available equipments, experiences,
funds, personalities, and so on. Nevertheless, we emphasize that evidence obtained
form a single approach generally cannot be considered definitive and requires the
support of data obtained by independent methods.
REFERENCES
1. Yagi T, Tokunaga T, Furuta Y, Nada S, Yoshida M, Tsukada T, Saga Y, Takeda N, Ikawa
Y, Aizawa S. 1993. A novel ES cell line, TT2, with high germline-differentiating potency.
Anal Biochem 214:70-76.
2. Tokunaga T, Tsunoda Y. 1992. Efficacious production of viable germ-line chimeras be-
tween embryonic stem (ES) cells and 8-cell stage embryos. Dev Growth Diff 34:561-566.
3. Nagy A, Rossant J, Nagy R, Abramow-Newerly W, Roder JC. 1993. Derivation of com-
pletely cell culture-derived mice from early-passage embryonic stem cells. Proc Natl Acad
Sci USA 90:8424-8428.
4. Soriano P, Montogomery C, Geske R, Bradley A. 1991. Targeted disruption of the c-src
proto-oncogene leads to osteopetrosis in mice. Cell 64:693-702.