Cytotoxicity of phenylpironetin analogs and the metabolic fate of pironetin and phenylpironetin.

To improve pironetin's metabolic stability we prepared four analogs by replacing its C12-14 segment with an aryl group. The antiproliferative activity of phenyl analog 4 was reduced two-fold and dihydroxy-4-fluorophenyl analog 5 was slightly more effective against OVCAR5 and A2780 ovarian cancer cell lines compared with the parent compound pironetin (1). The activity of 4-fluorophenyl analog 6 was reduced 3-fold in both cell lines. The activity of 7-O-methyl analog 7 was reduced 36-fold in OVCAR5 cells and 47-fold and A2780 cells, compared with pironetin. Phenylpironetin (4) was rapidly metabolized by mouse and human liver microsomes. We identified 17 human metabolites for phenyl analog 4 and 14 human metabolites for pironetin. Metabolism occurred at the C12-13 moiety, the α,ß-unsaturated lactone and the side chains of the molecules (C6-C11 segments). The significant extent of oxidative metabolism suggests that it may not be possible to attain a metabolically stable pironetin analog by structural modifications of the parent compound.

Revisiting microtubule targeting agents: α-Tubulin and the pironetin binding site as unexplored targets for cancer therapeutics.

Molecules that bind to tubulin and disrupt tubulin dynamics are known as microtubule targeting agents. Treatment with a microtubule targeting agent leads to cell cycle arrest followed by apoptosis. Tubulin inhibitors have been highly effective in the clinical treatment of a variety of tumors and are being investigated for treatment of several other diseases. Currently, all FDA approved microtubule inhibitors bind to ß-tubulin. Given the overall success of tubulin-binding agents in anticancer chemotherapy, α-tubulin is an attractive and unexplored target. Herein, we will discuss pironetin, the only compound known to bind α-tubulin, with particular focus on the known biological properties, the total syntheses, exploration of its structure-activity relationship, and future directions.

Identification of the Metabolic Profile of the α-Tubulin-Binding Natural Product (-)-Pironetin.

Pironetin, the only crystallographically confirmed natural product to target α-tubulin, displays potent cytotoxic activity against sensitive and resistant A2780 ovarian cancer cell lines but is only marginally active in vivo. We now report that pironetin has a short half-life (<7 min) in human liver microsomes, suggesting that its limited in vivo efficacy is due to rapid metabolism. Further, we describe the discovery of epoxypironetin as pironetin's major metabolite in human liver microsomes.

Multivalency amplifies the selection and affinity of bradykinin-derived peptides for lipid nanovesicles.

The trimer of a bradykinin derivative displayed a more than five-fold increase in binding affinity for phosphatidylserine-enriched nanovesicles as compared to its monomeric precursor. The nanovesicle selection is directly correlated with multivalency, which amplifies the electrostatic attraction. This strategy may lead to the development of novel molecular probes for detecting highly curved membrane bilayers.