Low generation PAMAM dendrimers as drug carriers for Pt(IV) complexes

An unsymmetrically carboxylated platinum(IV) analogue of oxaliplatin was coupled to low generation polyamidoamine dendrimers (PAMAM) with an amino-terminated surface (G-2; G-4). 1-D, 2-D diffusion NMR spectroscopy and high resolution HPLC-MS/MS were used to characterise the platinum complexes and drug-dendrimer conjugates. The average load of platinum(IV) complex per dendrimer was determined by ICP-MS, showing a maximum load of 38% (6 platinum units per dendrimer molecule) for the smaller G-2 generation and 34% (22 platinum units per dendrimer molecule) for G-4, respectively. As a result of this loading, the average diameter increased from 26 A to 34 A (30%, G-2) and from 46 A to 63 A (38%, G-4). The in vitro cytotoxicity of the free platinum(IV) complex, the complex loaded dendrimers and the free PAMAM analogues G-2 and G-4 was 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 the MTT assay. Whilst the free platinum(IV) compound displayed a rather moderate activity, the drug-dendrimer complexes showed a load and size dependent behaviour with IC50 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, according to results from the annexin V/PI assay for apoptosis/necrosis induction.