LST-2, a human liver-specific organic anion transporter determine smethotrexate sensitivity in the gastrointestinal cancers

Abstract

Background & Aims: One approach to the development of targeted cancer chemotherapy exploits increased uptake of the agent into neoplastic cells. In this scenario, higher concentrations of the agent in cancer cells are responsible for differential killing while the low concentration in normal human cells decreases side effects. The aim of this study is to isolate an organic anion transporter which is weakly in normal, but abundantly expressed in cancer cells, to deliver the anti-cancer drugs to the cells. Methods: A human liver cDNA library was screened with LST-1 cDNA as a probe. Northern blot analyses were performed using the isolated cDNA (termed LST-2). A LST-2 specific anitbody was raised and immunohistochemical analyses were performed. Xenopus oocyte expression system was used for functional analysis. We also established a permanent cell line which consistently expresses LST-2 to examine the relationship between MTX uptake and sensitivity. Results: The islated cDNA, LST-2 has 79.7 %.of overall homology with human LST-1. LST-2 exclusively expressed in the liver and its immunoreactiviy was highest at the basolateral membrane of the hepatocytes around the central vein. Although its weak expression in the liver, LST-2 is abundantly expressed in the gastric, colon and pancreatic cancers. On the other hand, the LST-1 was only detected in a hepatic cell line. LST-2 transports methotrexate in a saturable and dose dependent manner. Introduction of the LST-2 gene into mammalian cells potentiates sensitivity to methotrexate. Conclusion: LST-2 is a one of the prime candidate molecule for determining methotrexate sensitivity and may be a good target to deliver anti-cancer drugs to the gastrointestinal cancers.