Low-Generation Polyamidoamine Dendrimers as Drug Carriers for Platinum(IV) Complexes

An unsymmetrically carboxylated platinum(IV) analogue of oxaliplatin was coupled to low-generation polyamidoamine dendrimers (PAMAM) with amino-terminated surfaces [generations two (G-2) and four (G-4)]. 1D and 2D diffusion NMR spectroscopy and high-resolution HPLC–MS/MS were used to characterise the platinum complexes and drug–dendrimer conjugates. The average loads of platinum(IV) complex per dendrimer were determined by inductively coupled plasma MS (ICP-MS), and maximum loads of 38 % (six platinum units per dendrimer molecule) for the smaller G-2 and 34 % (22 platinum units per dendrimer molecule) for G-4 were obtained. As a result of this loading, the average diameters increased from 26 to 34 Å (30 %, G-2) and from 46 to 63 Å (38 %, G-4). The in vitro cytotoxicities of the free platinum(IV) complex, the complex-loaded dendrimers and the free PAMAM analogues G-2 and G-4 were evaluated in the cisplatin-sensitive ovarian cell line CH1/PA1 as well as in rather cisplatin-insensitive colon (SW480) and lung (A549) carcinoma cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Although the free platinum(IV) compound displayed a rather moderate activity, the drug–dendrimer complexes showed load- and size-dependent behaviour with IC ₅₀ values down to the low-nanomolar range. In the cisplatin-insensitive cell lines, the benefit of this platinum load primarily consists of added cytostatic rather than cytocidal effects, on the basis of the results from annexin V/PI (PI = propidium iodide) assays for apoptosis/necrosis induction.