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a Drug Discovery Program, Departments of Reproductive Biology,
b Chemistry, and
c Virology, Hughes Institute, St. Paul, Minnesota 55113
WHI-07, a novel bromo-methoxy-substituted aryl phosphate derivative of zidovudine (ZDV), is a potent dual-function contraceptive agent. Although the bromo-methoxy functional groups in the thymine ring of its ZDV are very important for its sperm-immobilizing activity (SIA), the importance of the esterification of the phosphate group with an amino acid side chain and the identity of the para substituent in the aryl moiety remain unclear. In the present study, we have synthesized 23 new analogues of WHI-07 by replacing the alanine (Ala) side chain with different amino acids containing nonpolar side chains, namely tryptophan (Trp), proline (Pro), phenylalanine (Phe), leucine (Leu), methionine (Met), valine (Val), or glycine (Gly). The para substituents on the aryl moiety included bromo, chloro, fluoro, nitro, or methoxy groups. The SIA of each of the 23 WHI-07 analogues was evaluated by computer-assisted sperm analysis. The potential cytotoxicity of these compounds against normal human ectocervical and endocervical epithelial cells was evaluated using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) cell viability assays. The replacement of the Ala side chain of WHI-07 with Val, Leu, or Phe led to a complete loss of SIA (EC50 values > 500 µM), whereas replacement with Trp reduced the SIA by 4-fold. The presence of para substituents on the phenyl moiety led to significant alterations in SIA. The anti-human immunodeficiency virus (HIV) activity of Trp-containing WHI-07 analogues was also diminished. Our finding highlights the necessity of Ala side chain and the presence of electron-withdrawing para-bromo substituent on the phenyl moiety in addition to bromo-methoxy functionalization groups on the thymine ring in order for the phosphoramidate derivatives of ZDV to be effective dual-function spermicidal agents. Unlike the detergent-type microbicide, nonoxynol-9, which was cytotoxic to normal human ectocervical and endocervical epithelial cells (IC50 values of 22 µM and 16 µM, respectively) at spermicidal concentrations (EC50 = 81 µM), WHI-07 and its active analogues were selectively spermicidal without cytotoxicity against female genital tract epithelial cells. WHI-07 and its Trp analogues hold particular clinical promise for the development of novel, nondetergent-type prophylactic contraceptives for the prevention of heterosexual HIV/acquired immunodeficiency syndrome transmission.
1 This work was supported in part by Grant RO1 HD37357 (O.J.D.) from the National Institutes of Health, National Institute of Child Health and Human Development, Bethesda, MD.
2 Correspondence: Osmond J. D'Cruz, Hughes Institute, 2665 Long Lake Road, Suite 330, St. Paul, MN 55113. FAX: 651 697 0645; odcruz{at}ih.org
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