Spermicidal activity of metallocene complexes containing vanadium(IV) in humans

We have used computer-assisted sperm analysis (CASA) to evaluate the spermicidal activity of 8 metallocene dihalides (vanadocene dichloride [VDC], titanocene dichloride [TDC], zirconocene dichloride [ZDC], molybdocene dichloride [MDC], hafnocene dichloride [HDC], vanadocene dibromide [VDB], bis[methylcyclopentadienyl] vanadium dichloride [VMDC], and vanadocene diiodide [VDI]); 5 vanadocene di-pseudohalides (vanadocene diazide [VDA], vanadocene dicyanide [VDCN], vanadocene dioxycyanate [VDOCN], vanadocene dithiocyanate [VDSCN], and vanadocene diselenocyanate [VDSeCN]); and 3 disubstituted derivatives (vanadocene ditriflate [VDT], vanadocene monochloro oxycyanate [VDCO], and vanadocene monochloro acetonitrilo tetrachloro ferrate [VDFe]). Whereas the metallocene complexes containing titanium, zirconium, molybdenum, and hafnodium were inactive, all 12 vanadocene complexes elicited potent spermicidal activity at nano-micromolar concentrations with an order of efficacy VDSeCN > VDSCN > VDB > VMDC > VDCN > VDA > VDC > VDOCN > VDI > VDT > VDFe > VDCO without disrupting the acrosomal membrane, as determined by high-resolution low-voltage scanning electron microscopy. The sperm-immobilizing activity of the vanadocene complexes was rapid and irreversible, since the treated sperm underwent apoptosis as determined by the flow cytometric annexin V binding assay, DNA nick end-labeling, and confocal laser scanning microscopy. These results provide unprecedented evidence that metallocene complexes containing vanadium(IV), especially VDSeCN, may be useful as contraceptive agents.