Potent Platinum(IV) Prodrugs That Incorporate a Biotin Moiety to Selectively Target Cancer Cells.

Four platinum(IV) prodrugs incorporating a biotin moiety to selectively target cancer cells were synthesised, characterised, and their biological activity assessed. All complexes exhibited exceptional in vitro cytotoxicity against a panel of cancer cell lines, with [Pt(5,6-dimethyl-1,10-phenanthroline)(1 S ,2 S -diaminocyclohexane)(biotin)(hydroxido)](NO 3 ) 2 , ( 2 ) exhibiting the lowest GI 50 of 4 nM in the prostate Du145 cancer cell line. Each complex displayed significantly enhanced activity compared to cisplatin, with 2 being 1000-fold more active in the HT29 colon cancer cell line. Against the MCF-7 breast cancer cell line, in which high levels of biotin receptors are expressed, 2 , [Pt(4,7-dimethoxy-1,10-phenanthroline)(1 S ,2 S -diaminocyclohexane)(biotin)(hydroxido)](NO 3 ) 2 , ( 3 ), and [Pt(5-methyl-1,10-phenanthroline)(1 S ,2 S -diaminocyclohexane)(biotin)(hydroxido)](NO 3 ) 2 , ( 4 ) exhibited enhanced activity compared to their platinum(II) cores, with 4 being 6-fold more active than its platinum(II) precursor. Furthermore, 3 exhibited 3-fold greater selectivity towards MCF-7 breast cancer cells compared to MCF10A breast healthy cells, and this was further confirmed by platinum uptake studies, which showed 3 to have almost 3-fold greater uptake in MCF-7 cells, compared to MCF10A cells. The results show that lipophilicity and selectivity both contributed to the cellular uptake of 1 - 4 ; however, this was not always translated to the observed cytotoxicity.