For example, the antiproliferative effect of copper(II) complexes results from the inhibition of the activities of enzymes, which play a pivotal role in cancer therapy, e.g., protein disulfide isomerase (PDI) [20], topoisomerases I and II [21,22,23], telomerase [24] or proteasome [25,26,27], as well as DNA intercalation [28,29,30] and DNA degradation [31,32]. Here, P4HB is linked to cancer.