Although the
platinum-based anticancer drugs
cisplatin,
carboplatin, and
oxaliplatin have similar
DNA-binding properties, only
oxaliplatin is active against
colorectal tumors. The mechanisms for this
tumor specificity of
platinum-based compounds are poorly understood but could be related to differences in uptake. This study shows that the human organic
cation transporters (OCT) 1 and 2 (SLC22A1 and SLC22A2) markedly increase
oxaliplatin, but not
cisplatin or
carboplatin, accumulation and cytotoxicity in transfected cells, indicating that
oxaliplatin is an excellent substrate of these transporters. The cytotoxicity of
oxaliplatin was greater than that of
cisplatin in six
colon cancer cell lines [mean +/- SE of IC(50) in the six cell lines, 3.9 +/- 1.4 micromol/L (
oxaliplatin) versus 11 +/- 2.0 micromol/L (
cisplatin)] but was reduced by an OCT inhibitor,
cimetidine, to a level similar to, or even lower than that of,
cisplatin (29 +/- 11 micromol/L for
oxaliplatin versus 19 +/- 4.3 micromol/L for
cisplatin). Structure-activity studies indicated that organic functionalities on nonleaving groups coordinated to
platinum are critical for selective uptake by OCTs. These results indicate that OCT1 and OCT2 are major determinants of the anticancer activity of
oxaliplatin and may contribute to its antitumor specificity. They also strongly suggest that expression of OCTs in
tumors should be investigated as markers for selecting specific
platinum-based
therapies in individual patients. The development of new anticancer drugs, specifically targeted to OCTs, represents a novel strategy for targeted
drug therapy. The results of the present structure-activity studies indicate specific tactics for realizing this goal.