N1-substituent effects in the selective delivery of polyamine conjugates into cells containing active polyamine transporters

Several N-1-arylalkylpolyamines containing various aromatic ring systems were synthesized as their respective HCI salts. The N-1-substituents evaluated ranged in size from N-1-benzyl, N-1-naphthalen-1-ylmethyl, N-1-2-(naphthalen-1-yl)ethyl, N-1-3-(naphthalen-1-yl)propyl, N(1)anthracen-9-ylmethyl, N-1-2-(anthracen-9-yl)ethyl, N-1-3-(anthracen-9-yl)propyl, and pyren-1-ylmethyl. The polyamine architecture was also altered and ranged from diamine to triamine and tetraamine systems. Biological activities in L1210 (murine leukemia), Chinese hamster ovary (CHO), and CHO's polyamine transport-deficient mutant (CHO-MG) cell lines were investigated via IC50 cytotoxicity determinations. K-i values for spermidine uptake were also determined in L1210 cells. The size of the N-1-arylalkyl substituent as well as the polyamine sequence used had direct bearing on the observed cytotoxicity profiles. N-1-Tethers longer than ethylene showed dramatic loss of selectivity for the polyamine transporter (PAT) as shown in a CHO/CHO-MG cytotoxicity screen. In summary, there are clear limits to the size of N(1-)substituents, which can be accommodated by the polyamine transporter. A direct correlation was observed between polyamine-conjugate uptake and cytotoxicity. In this regard, a cytotoxicity model was proposed, which describes a hydrophobic pocket of set dimensions adjacent to the putative PAT polyamine-binding site.