PT - JOURNAL ARTICLE AU - Angelica M. Merlot AU - Namfon Pantarat AU - Sharleen V. Menezes AU - Sumit Sahni AU - Des R. Richardson AU - Danuta S. Kalinowski TI - Cellular Uptake of the Anti-Tumor and Anti-Metastatic Agent, Dp44mT, Occurs <em>via</em> a Saturable, Temperature-Dependent Mechanism Consistent with Carrier/Receptor-Mediated Transport AID - 10.1124/mol.113.088393 DP - 2013 Oct 01 TA - Molecular Pharmacology PG - mol.113.088393 4099 - http://molpharm.aspetjournals.org/content/early/2013/10/01/mol.113.088393.short 4100 - http://molpharm.aspetjournals.org/content/early/2013/10/01/mol.113.088393.full AB - The chelator, di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT), shows potent and selective anti-cancer and anti-metastatic activity. However, the mechanism by which it is initially transported into cells to induce cytotoxicity is unknown. Hence, the current investigation examined the cellular uptake of 14C-Dp44mT relative to two structurally-related ligands, namely the aroylhydrazone, 14C-pyridoxal isonicotinoyl hydrazone (14C-PIH), and the thiosemicarbazone, 14C-2-benzoylpyridine-4-ethyl-3-thiosemicarbazone (14C-Bp4eT). In marked contrast to the cellular uptake of 14C-PIH and 14C-Bp4eT that were linear as a function of concentration, 14C-Dp44mT uptake was saturable in SK-N-MC neuroepithelioma cells (Bmax 4.28 x 107 molecules of chelator/cell and Kd 2.45 μM). Together with the fact that 14C-Dp44mT uptake was temperature-dependent and significantly (p &lt; 0.01) decreased by competing unlabeled Dp44mT, these observations indicated a saturable transport mechanism consistent with carrier/receptor-mediated transport. Other unlabeled ligands that shared the saturated N4 structural moiety with Dp44mT significantly (p &lt; 0.01) inhibited 14C-Dp44mT uptake, demonstrating its importance for carrier/receptor recognition. Nevertheless, unlabeled Dp44mT most markedly decreased 14C-Dp44mT uptake, demonstrating that the putative carrier/receptor shows high selectivity for Dp44mT. Interestingly, in contrast to 14C-Dp44mT, uptake of its Fe complex [Fe(14C-Dp44mT) 2] was not saturable as a function of concentration and was much greater than the ligand alone, indicating an alternate mode of transport. Studies examining the tissue distribution of 14C-Dp44mT injected intravenously into a mouse tumor model demonstrated the 14C label was primarily identified in the excretory system. Collectively, these findings examining the mechanism of Dp44mT uptake and its distribution and excretion have clinical implications for the bioavailability and uptake of the agent in vivo.