ABSTRACT
E7974 is a synthetic analogue of the marine sponge natural product hemiasterlin. Here, we show that E7974, such as parental hemiasterlin, acts via a tubulin-based antimitotic mechanism. E7974 inhibits polymerization of purified tubulin in vitro with IC(50) values similar to those of vinblastine. In cultured human cancer cells, E7974 induces G(2)-M arrest and marked disruption of mitotic spindle formation characteristic of tubulin-targeted anticancer drugs. Extensive hypodiploid cell populations are seen in E7974-treated cells, indicating initiation of apoptosis after prolonged G(2)-M blockage. Consistent with this observation, E7974 induces caspase-3 activation and poly ADP ribose polymerase cleavage, typical biochemical markers of apoptosis. Only a short cellular exposure to E7974 is sufficient to induce maximum mitotic arrest, suggesting that E7974's antitumor effects in vivo may persist even after blood levels of the drug decrease after drug administration. Interactions of E7974 with purified tubulin were investigated using two synthetic tritiated photoaffinity analogues incorporating a benzophenone photoaffinity moiety at two different positions of the E7974 scaffold. Both analogues preferentially photolabeled alpha-tubulin, although minor binding to beta-tubulin was also detected. E7974 thus seems to share a unique, predominantly alpha-tubulin-targeted mechanism with other hemiasterlin-based compounds, suggesting that, unlike many tubulin-targeted natural products and related drugs, the hemiasterlins evolved to mainly target alpha-tubulin, not beta-tubulin subunits.
Subject(s)
Antimitotic Agents/pharmacology , Antineoplastic Agents/pharmacology , Biological Products/chemistry , Oligopeptides/chemistry , Oligopeptides/pharmacology , Piperidines/pharmacology , Porifera/chemistry , Seawater , Tubulin/metabolism , Animals , Antimitotic Agents/chemistry , Antineoplastic Agents/chemistry , Apoptosis/drug effects , Biological Products/pharmacology , Cattle , Cell Line, Tumor , G2 Phase/drug effects , Humans , Microtubules/drug effects , Microtubules/metabolism , Mitosis/drug effects , Photoaffinity Labels , Piperidines/chemistry , Spindle Apparatus/drug effects , Spindle Apparatus/metabolism , Vinblastine/pharmacologyABSTRACT
Novel synthetic phospholipid compound 1 was discovered to be an antagonist of human toll-like receptor 2 (TLR2) signaling. In a preliminary SAR campaign we synthesized several analogues of 1 and found that considerable structural changes could be made without loss of TLR2 antagonistic activity.
