Design, synthesis, and evaluation of pH-dependent hydrolyzable emetine analogues as treatment for prostate cancer

The N-2′ position of the natural product emetine has been derivatized to thiourea, urea, sulfonamide, dithiocarbamate, carbamate, and pH responsive hydrolyzable amide analogues. In vitro studies of these analogues in PC3 and LNCaP prostate cancer cell lines showed that the analogues are generally less cytotoxic (average IC₅₀ ranging from 0.079 to 10 μM) than emetine (IC₅₀ ranging from 0.0237 to 0.0329 μM). The pH sensitive sodium dithiocarbamate salt 13 and the amide analogues 21, 22, 26 (obtained from maleic and citraconic anhydrides) showed the most promise as acid-activatable prodrugs under mildly acidic conditions found in the cancer microenvironment. These prodrugs released 12-83% of emetine at pH 6.5 and 41-95% emetine at pH 5.5. Compounds 13 and 26 were further shown to exhibit increased cytotoxicity in PC3 cell culture medium that was already below pH 7.0 at the time of treatment.