ZYN-LINKED COLCHICINES - CONTROLLED-RELEASE LIPOPHILIC PRODRUGS WITH ENHANCED ANTITUMOR EFFICACY

Conjugation of antimitotic colchicine derivatives with proprietary lip ophilic molecules (Zyn-Linkers(TM)) via acid cleavable linkages (hydra zone or imine) produced prodrugs with enhanced antitumor activity. The pharmacodynamic properties (half-lives) of the pH-sensitive linkages were determined around values which might be expected in intracellular , especially lysosomal, environments. In buffered solutions at pH 4.1, 5.6, and 7.2, conjugates released 50% of the drug at rates from 0.1 h at pH 4.1 to over 3 months at neutral pH. In a tumor cell cytotoxicit y assay, the slowest releasing molecules were up to 100-fold less acti ve in vitro than the unlinked drug, which demonstrated that the Linkag es were stable and that a true prodrug had been generated. Binding of conjugate to cells, release of active drug and action on an intracellu lar target (tubulin) were demonstrated by the ability of the conjugate s to block cells in the G2/M phase of the cell cycle 20 h after a 10 m in exposure and was consistent with the rate of drug released. In vivo , a single injection of the Zyn-Linked conjugated colchicines enhanced the survival time of the mice to a greater extent than single doses o f the unlinked colchicine analogues in a murine tumor model. Activity of the slowest releasing conjugate (ZYN 162) was shown to be comparabl e to a single LD(10) dose of doxorubicin. These data suggest that the Zyn-Linker conjugates described containing acid cleavable bonds form a body depot of prodrug which release an anti-mitotic agent and can sig nificantly inhibit tumor growth.