Cisplatin has been known as an anticancer drug for a long time. It is therapeutically active upon binding to DNA. A double-bound cisplatin bends DNA into a localized kink. We model the elastic properties of cisplatin-DNA adducts at moderate tension (<6 pN). It is shown that from the mechanical point of view the action of cisplatin can be revealed by reduced persistence length. We derived two expressions for the persistence length, which apply in the linear-response and the strong-force regimes, respectively. Experimental data for DNA adducts stretched by magnetic tweezers are consistently fitted by these expressions. This allows us to estimate the degree of platination at various salt concentrations.