Several abietane diterpenes of the royleanone and coleon type have been described as antimicrobial [1], [2], [3], antifungal [1], [2],[4],andantitumoral[4],[5]activemetabolites.Inthepastwe reportedtheantimicrobialactivityofseveralroyleanonesisolated from Plectranthus hereroensis [1]and P. grandidentatus [2].Further studiesontheconstituentsof P. grandidentatus resultedintheiso- lationoffiveknowncompounds:fattyacidestersof7a-acyloxy- 6b-hydroxyroyleanone (1) [2], grandidone A (2)[6],7a-acetoxy- 6b-hydroxyroyleanone(3)[7],6b,7a-dihydroxyroyleanone(4)[7], andcoleonU(5)[8].Thestructuresoftheseabietaneswerecon- firmed by comparing their physical and spectroscopic data with thosereportedintheliterature.Herewedescribethe in vitro effect of these abietanes on the growth of five human cancer cell lines MCF-7(breast),NCI-H460(lung),SF-268(CNS),TK-10(renal)and UACC-62(melanoma).TheresultsaresummarisedinTable 1 . Diterpenes 2, 3, 4 and 5 inhibited the growth of all cancer cell lines, after 48h of continuous exposure, in a dose-dependent way.Compound 1 wasfoundtobeinactive,evenwhentestedat 50 mg/ml. Whilecompounds 2 and 4 showed,ingeneral,apoorinhibitory effect(GI 50 >20 mM),compounds 3 and 5 werefoundtobepotent inhibitorsofthegrowthofthefivehumancancercelllines(GI 50 < 10 mM).Compound 5 exhibitedthestrongesteffectamongallthe abietanediterpenestested,showingGI 50 valuesthatrangefrom 2.5 mMto5.5 mM. Although no significant cell type selectivity wasobservedwiththeabietanestested,compound 2 wasfound tobemoreactiveagainsttheMCF-7celllines. The antiproliferative effect showed by the abietane diterpenes studiedseemstobeduetogrowtharrestandnottocelldeath (cytotoxicity). In the SRB assay, the number of cells that re- mained after the 48h exposure period was not inferior to the number of cells before the treatment. Studies of viability, per- formed by trypan blue assay on the well characterised human breastcellline(MCF-7)withthemostpotentcompounds 3 and 5,confirmedthisfinding.TheviabilityofMCF-7cellsaftertreat- mentwith 3 and 5 attheirsGI 50 concentrationsfor48hwas80% and90%,respectively. The comparison of the growth inhibitory effects of monomeric royleanones(1 , 3 and 4)andcoleon 5 ledustothinkthatlipophi- licitymayperformaroleinthecellmembranepenetration.Acety- lated abietane 3 shows a stronger antiproliferative activity than abietane 4,whichhasthehydroxygroupatC-7free.Compound 4 seemstogothroughthecellmembranelesseffectively,inthetest systemused.Oneexplanationforthisisthatacetylationcausesan increase of lipophilicity, and so may enhance its permeability through cellular membranes. However the presence of a fatty acidchain,increasingevenmorethelipophilicity,hadanegative influenceintheinhibitoryeffectofcompound 1 .Thepresenceof intramolecularhydrogenbondingsmayincreasethelipophilicity of coleon U (5), which contains no ester group and shows the strongestactivity.Dimer 2 (aketalof6,7-dioxoroyleanoneandco- EffectofAbietaneDiterpenesfrom Plectranthus grandidentatus onthe GrowthofHumanCancerCellLines Cristina Gaspar Marques 1 , Madalena Pedro 2 , M. Fµtima A. Simðes 1 , Maria So JosØ Nascimento 2 , Madalena M. M. Pinto 2 , Benjamín Rodríguez 3 Affiliation: 1 FaculdadedeFarmµciadaUniversidadedeLisboa,CECF,Lisboa, Portugal ´ 2 CentrodeEstudosdeQuímicaOrgânica,FitoquímicaeFarmacolo- giadaUniversidadedoPorto,FaculdadedeFarmµcia,Porto,Portugal´ 3 Insti- tutodeQuímicaOrgµnica,CSIC,Madrid,Spain Correspondence: Dr.Mã.FµtimaA.Simðes´FaculdadedeFarmµcia´Universi- dadedeLisboa-CECF´Av.dasForc ËasArmadas´1649-019Lisboa,Portugal´E- Mail:fasimoes@ff.ul.pt´Fax:351-217946470 Received: January25,2002´ Accepted: April11,2002 Bibliography: PlantaMed2002;68:839±840´GeorgThiemeVerlagStuttgart´ NewYork´ISSN0032-0943 Abstract Fiveknownabietanediterpenes,fattyacidestersof7a-acyloxy- 6b-hydroxyroyleanone(1),grandidoneA(2),7a-acetoxy-6b-hy- droxyroyleanone(3),6b,7a-dihydroxyroyleanone(4),andcoleon U(5), isolated from Plectranthus grandidentatus Gürke, were evaluated for their in vitro antiproliferative activityagainst five human cancer cell lines MCF-7, NCI-H460, SF-268, TK-10, and UACC-62. Coleon U (5) exhibited the strongest effect among all theassayedcompounds.Theabietane 3 revealedalsoastrongin- hibitory effect while diterpenes 2 and 4 inhibited only slightly thegrowthofallcancercelllines. Table 1 Concentration of compounds causing 50% cell growth inhibi- tion (GI 50 ) of five human cancer cell lines Compounds GI 50 (mM) MCF-7 NCI-H460 SF-268 TK-10 UACC-62 1 >50* >50* >50* >50* >50* 2 9.6  1.8 19.2  3.1 25.8  4.0 40.9  3.7 35.7  1.5 3 6.4  0.4 3.0  0.3 8.6  1.1 7.4  0.6 4.5  0.7 4 48.3  4.3 39.2  2.3 70.8  8.2 107.6  1.4 77.9  8.6 5 5.5  0.8 3.0  0.2 4.2  0.9 3.5  0.1 2.5  0.3 Doxorubicin (nM) 55.0  32 81  2.0 93.0  7.0 570.0  132 94.0  9.4 Doxorubicin was used as positive control. *Values in mg/ml. Results show means  SEM of 3±6 independent observations performed in duplicate. Letter 839 Downloaded by: University of Pittsburgh. Copyrighted material.