Automated parallel solid-phase synthesis and anticancer screening of a library of peptide-tethered platinum(II) complexes

The automated parallel solid-phase synthesis of a 36-member library of peptide-tethered platinum(II) complexes is described. The identity and quality of each product were confirmed by mass spectrometry and H-1 NMR. Subsequently, each compound was screened for in vitro anticancer activity by treating the A2780 (human ovarian carcinoma) cell line with two concentrations of the drugs (100 and 10 muM) in quadruplicate. The reduction of cell proliferation induced by the drugs at these concentrations was determined with the MTT colorimetric assay (MTT = 3-(4',5'-dimethylthiazol-2'-yl)-2,5-diphenyltetrazolium bromide) and compared to cisplatin. Even though no very active library members could be identified, five apparently most active (8{1}, 8{4}, 8{10}, 8{13}, and 8{24}) and two inactive complexes (8{33} and 8{34}) were purified using gel permeation chromatography and fully characterized by NMR spectroscopy (H-1, Pt-195) and MS. The IC50 values of these complexes and cisplatin in A2780 cells were subsequently determined using the MTT assay in a conventional manner. All seven complexes have an IC50 above 100 muM, confirming the results generated by the assay at 100 and 10 muM of the crude reaction products.