Studies in humans on the mechanism of potent spermicidal and apoptosis-inducing activities of vanadocene complexes.
We previously demonstrated that bis-cyclopentadienyl (Cp) complexes of vanadium(IV) (vanadocenes) are potent spermicidal and apoptosis-inducing agents. To gain further insight into the structure-function relationships controlling these two properties of vanadocenes, we have synthesized analogues in which the bis-Cp rings were substituted with one or five electron-donating methyl groups. The three complexes included vanadocene dichloride (VDC), bis(methylcyclopentadienyl) vanadium dichloride (VMDC), and bis(pentamethylcyclopentadienyl) vanadium dichloride (VPMDC). The concentration-dependent effect of these vanadocenes on sperm-immobilizing activity (SIA), mitochondrial membrane potential (DeltaPsim), axonemal dynein ATPase activity, and tyrosine phosphorylation of global and axoneme-specific sperm proteins was assessed by computer-assisted sperm analysis, flow cytometry, colorimetry, and immunoblotting, respectively. Apoptosis-inducing ability was quantitated by the two-color flow cytometric terminal dideoxynucleotidyl transferase-based assay that labels 3'-hydroxyl ends of fragmented DNA. All three vanadocenes induced rapid sperm immobilization (T(1/2) < 15 sec). Substitution of the bis-Cp rings by five methyl groups augmented the SIA of VDC by 10-fold. The EC(50) values (50% inhibitory concentration) for VDC, VMDC, and VPMDC were 7.5 microM, 4.3 microM, and 0.7 microM, respectively. Whereas SIA of vanadocenes was apparent at low micromolar concentrations, the apoptosis-inducing property was evident only at higher micromolar concentrations. The concentrations of VDC, VMDC, and VPMDC required for 50% apoptosis were 49 microM, 67 microM, and 153 microM, and for 50% reduction in sperm DeltaPsim were 435 microM, 173 microM, and 124 microM, respectively. Spermicidal activity of vanadocenes was not dependent on the inhibition of ATPase or tyrosine phosphorylation of global and sperm axonemal proteins. Due to the ability of these vanadocene complexes to rapidly generate hydroxyl radicals in the presence of oxidant, our findings provide unprecedented evidence for a novel mechanism of action for spermicidal vanadocenes. The differential concentration-dependent spermicidal and apoptosis-inducing properties of vanadocenes gives them particular utility as a new class of vaginal contraceptives.
D'Cruz
O J
OJ
Drug Discovery Program, Departments of Reproductive Biology and Biochemistry, Parker Hughes Institute, St. Paul, Minnesota 55113, USA. odcruz@ih.org
Vassilev
A
A
Uckun
F M
FM
D017209:Apoptosis / Q000187:drug effects*; D001696:Biomechanical Phenomena; D015153:Blotting, Western; D004396:Coloring Agents; D053938:DNA Fragmentation / Q000187:drug effects; D004398:Dyneins / Q000378:metabolism; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D020287:In Situ Nick-End Labeling; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010710:Phosphates / Q000378:metabolism; D019000:Phosphotyrosine / Q000037:antagonists & inhibitors; D013081:Sperm Motility / Q000187:drug effects; D013089:Spermatocidal Agents / Q000494:pharmacology*; D013094:Spermatozoa / Q000187:drug effects* / Q000648:ultrastructure; D013329:Structure-Activity Relationship; D013778:Tetrazolium Salts; D013844:Thiazoles; D014621:Vagina / Q000166:cytology / Q000187:drug effects; D017968:Vanadium Compounds / Q000494:pharmacology*
D004396:Coloring Agents; D010710:Phosphates; D013089:Spermatocidal Agents; D013778:Tetrazolium Salts; D013844:Thiazoles; D017968:Vanadium Compounds; D019000:Phosphotyrosine; C030754:vanadocene dichloride; D004398:Dyneins; C022616:thiazolyl blue