Effect of propolis extract on malignant cell transformation by moloney murine sarcoma virus

An aqueous extract of propolis was found to significantly inhibit NIH/3T3 c ell malignant transformation by Moloney murine sarcoma virus (MuSV 124). Th e inhibitory effect of propolis extract was most effective when it was adde d 2 h before infection or at the time of infection. The continuous presence of propolis extract in the culture medium was essential for full preventio n of malignant cell transformation. When treatment with propolis extract wa s terminated, five to ten days post-infection, there was a significant reco very in cell transformation. These results suggest that propolis extract in hibits a late step after provirus integration into the host genome. Additio n of propolis extract after infection with MuSV significantly inhibited cel l transformation. The inhibitory effect of propolis appeared to be the resu lt of the inhibition of primary - not secondary - infections, since MuSV-12 4 yields a virus-nonproducing infection.