In vitro testing of rationally designed spermicides for selectively targeting human sperm in vagina to ensure safe contraception.

BACKGROUND Rational synthesis of novel structures resulted in two unique molecules (DSE-36 and DSE-37, disulphide esters of carbothioic acid) that killed sperm 25 times more strongly and with a precisely targeted action than nonoxynol-9 (N-9). We examine the effects of DSE-36 and DSE-37 on human spermatozoa versus HeLa cells to establish specificity and safety compared with N-9. METHODS AND RESULTS At spermicidal EC(100) (20 microg/ml) DSE-36 and DSE-37 killed 100% sperm in <30 s (Sander-Cramer assay) and at EC(50) induced apoptosis in sperm (Annexin-V-fluorescein isothiocyanate and JC-1 labelling and Flow Cytometry) in 3 h. However, at EC(100) these molecules had no effect on HeLa cells by 24 h or on cell viability [3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay], surface ultrastructure (scanning electron microscopy), Annexin-V and JC-1 labelling pattern and reactive oxygen species (ROS) generation. N-9, with a spermicidal EC(100) of 500 microg/ml, decreased HeLa cell viability at 20 microg/ml in 24 h (P < 0.001), accompanied by acute damage to cell surface ultrastructural topography, induction of apoptosis and ROS generation. Unlike DSE-36 and DSE-37, N-9 also significantly induced mRNA levels (RT-PCR) of pro-inflammatory biomarkers (interleukin (IL)-1 alpha, IL-6, IL-8, RANTES) in HeLa cells and increased IL-6 and IL-8 secretion (P < 0.001, enzyme-linked immunosorbent assay). Furthermore, DSE-36 and DSE-37 did not inhibit Lactobacillus growth at EC(100) and exhibited mild microbicidal activity against Trichomonas vaginalis, while N-9 inhibited Lactobacillus and Trichomonas growth but had a lower prophylactic index. CONCLUSIONS The ability of these novel spermicides to kill sperm almost instantaneously at innocuously low concentration indicates their worth as improved active ingredients for vaginal contraceptive preparations compared with N-9.