Revisiting [PtCl2(cis-1,4-DACH)]: An Underestimated Antitumor Drug with Potential Application to the Treatment of Oxaliplatin-Refractory Colorectal Cancer

Although the encouraging antitumor activity of [PtCl2(cis-1,4-DACH)] (1; DACH = diaminocyclohexane) was shown in early studies almost 20 years ago, the compound has remained nearly neglected. In contrast, oxaliplatin, containing the isomeric 1(R),2(R)DACH carrier ligand, enjoys worldwide clinic application as a most important therapeutic agent in the treatment of colorectal cancer. By extending the investigation to human chemotherapy-resistant cancer cells, we have demonstrated the real effectiveness of 1 in circumventing cisplatin and oxaliplatin resistance in LoVo colon cancer cells. The uptake of compound 1 by the latter cells was similar to that of sensitive LoVo cells. This is not the case for all other compounds considered in this investigation. Interaction with double-stranded DNA, investigated by a biosensor assay and by quantum mechanical/molecular mechanical geometry optimization of the 1,2-GG intrastrand cross-link, does not show significant differences between 1 and oxaliplatin. However, the DNA adducts of 1 are removed from repair systems with lower efficiency and are more effective in inhibiting DNA and RNA polymerase.