190 Bulgarian Journal of Agricultural Science, 19 (2) 2013, 190–193 Agricultural Academy COMPARATIVE ANTI-HERPES EFFECTS OF THE CHLOROFORM IN VITRO AND IN VIVO EXTRACTS, DERIVED FROM LAMIUM ALBUM L. D. TODOROV 1 , M. DIMITROVA 2 , K. SHISHKOVA 1 , Zh. YORDANOVA 2 , V. KAPCHINA-TOTEVA 2 and S. SHISHKOV 1 1 Sofia University “St. Kl. Ohridski”, Laboratory of Virology, BG – 1164 Sofia, Bulgaria 2 Sofia University “St. Kl. Ohridski”, Department of Plant Physiology, Faculty of Biology, BG – 1164 Sofia, Bulgaria Abstract TODOROV, D., M. DIMITROVA, K. SHISHKOVA, ZH. YORDANOVA, V. KAPCHINA-TOTEVA and S. SHISHKOV, 2013. Comparative anti-herpes effects of the chloroform in vitro and in vivo extracts, derived from Lamium album L. Bulg. J. Agric. Sci., Supplement 2, 19: 190–193 Lamium album L. is a valuable medicinal plant which possesses astringent, spasmolytic, anti-inflammatory, antibiotic and bacteriostatic properties. In our study, chloroform extracts derived by Soxhlet extraction from in vivo and in vitro propagated plants were tested for antiviral activity. The extracts inhibited significantly the replication of herpes simplex virus type 1 (HSV- 1) and type 2 (HSV-2) in MDBK cells, without apparent cytotoxicity. The extracts showed strong antiviral effect. The 50% inhibitory concentrations (IC 50 ) of the chloroform in vitro extract (CS) were 552μg.mL –1 and 487μg.mL –1 , respectively. The IC 50 of the chloroform in vivo extract (CES) were 668μg.mL –1 and 780μg.mL –1 , respectively. Viral replication was suppressed over 90% when both chloroform extracts were applied at maximal tolerated concentrations (MTC). The data suggested that extracts derived from wild plants have stronger inhibitory effects than in vitro extracts. The chloroform in vivo extract CES showed strong virucidal effect. The extract applied in MTC inactivated the extracellular HSV-1 after 5 minutes of contact at a rate exceeding 90% (∆log1.5). Key words: in vitro and in vivo extracts, Lamium album, herpes simplex virus, viral inhibitor, virucidal effect Abbreviations: CS – chloroform in vitro extract, CES – chloroform in vivo extract *E-mail: sashishkov@yahoo.com Introduction Herpes simplex viruses type 1 and type 2 are impor- tant widespread human pathogens (Khan, 2005; Xu et al., 2006). Antiviral chemotherapy is a standard practice in the management of herpesvirus infections in humans, and currently there are about 11 licensed anti-herpetic drugs available (De Clercq et al., 2006). The most commonly used ones are the nucleoside analog acyclovir, its deriva- tives and cidofovir (Elion, 1993). These drugs have been well established for over two decades, however, continu- ous therapy leads to the development of resistant strains (Bacon et al., 2003). Current data indicate the existence of mutant clinical strains, with cross-resistance and double- crossed resistance against these antiviral drugs (Sarasini et al., 1995). That is why the search for new therapeutic agents is an ongoing process. A special attention is focused on compounds with natural origin. The advantages of this kind of compounds over the synthetic drugs are that the oc- currence of resistant strains against their action is delayed due to their complex chemical structure and their lower cy- totoxicity Many natural active compounds have been iden- tified worldwide (Harvey, 2000; Newman, 2007; Istatkova et al., 2012). Therefore, natural products, including tradi- tional medicinal plants, are promising potential sources of new effective antiviral drugs.