Delineation of therapeutic significance of transporters as molecular targets of drugs

Transporters are membrane proteins mediating permeation of organic and inorganic solutes through the plasma membrane and membranes of intracellular organella. They play essential roles in the epithelial absorption and cellular uptake of nutrients as well as absorption, distribution, metabolism and excretion of drugs. Because transporters contribute to determine the distribution of compounds in the body in concert with metabolic/synthetic enzymes, the drugs that affect the functions of transporters are expected to alter the distribution of compounds in the body and to ameliorate disrupted homeostasis. In this context, drugs targeting transporters have been used clinically. Such drugs include antidepressants targeting monoamine transporters, diuretics targeting inorganic ion transporters of renal tubules and uricosuric agents targeting renal urate transporters. Now new transporter-targeting drugs designed based on post-genome drug development strategy have been in the process of clinical trials or basic/clinical researches. For example, the inhibitors of renal Na⁺/glucose cotransporter SGLT2 have been proved for its efficacy in the treatment of diabetes mellitus. The cancer type amino acid transporter LAT1 has been considered as a target of cancer diagnosis and therapeutics. The transporter-targeting drugs are expected to provide new rationale in the therapeutics of various diseases.