## 3 S. sclarea Roots Contain Bioactive Abietane Diterpenes  
_Salvia sclarea_ (clary sage) is a biennial or perennial plant belonging to the Lamiaceae family, typical of the north of the Mediterranean, central Asia, and some areas of North Africa. It is well known for the extraction of sclareol produced in the flower calves, which is used for the semi-synthesis of the ambroxide, a well-prized perfume ingredient. This compound derives by the cyclization of GGPP by a Labd-13-en-8-ol diphosphate synthase (SsLPPS) to labda-13-en-8-ol diphosphate (LPP), which is subsequently converted into sclareol [16]. However, interesting additional abietane-quinone-type diterpenes are synthesized in the roots of _S. sclarea_, such as carnosic acid, aethiopinone, 1-oxoaethiopinone, salvipisone, and ferruginol, with known pharmacological properties, summarized in Table 1. Aethiopinone, salvipisone, 1-oxoaethiopinone, and ferruginol, from _S. sclarea_,  
Figure 2: Diagram representing bibliographic research criteria used for this review. showed bacteriostatic as well as bactericidal activities against different strains of _Staphylococcus aureus_ and _Staphylococcus epidermidis_, through a synergistic action of salvipsone and aethiopinone with \(\delta\)-lactam antibiotics [17]. Cytotoxic and antitumor activities in several human tumor cell lines have been reported for tricyclic diterpenoids [9; 18; 19], especially those containing quinone moiety, often present in several effective cancer chemotherapeutic agents [20]. Salvipsione and aethiopinone showed relatively high cytotoxicity against HL-60 and NALM-6 leukemia cells, by inducing a caspase-3-mediated apoptosis [19]. In addition, our studies have contributed to establish that aethiopinone, purified from _S. sclarea_ hairy roots, has also cytotoxic different and anti-proliferative activities against other tumor cells, in particular against solid tumor cell lines, such as MCF7 (breast adenocarcinoma), HeLa (epithelial carcinoma), PC3 (prostate adenocarcinoma), and A375 (human melanoma), for which drug resistance is often reported [21], and with negligible effects in non-tumor cells [9]. Especially interesting is this anti-melanoma activity exerted by aethiopinone, since melanoma cells are intrinsically resistant to pharmacological anticancer treatment and pharmaceutical companies are searching for more active and stable drugs [21]. One drawback in using these interesting compounds as potential new anti-tumor drugs is their very low amount (<0.5% dry weight) in natural and cultivated plants, as reported frequently for most of the plant secondary metabolites [1]. Plant cell and tissue cultures have been largely considered an attractive possibility of extraction of plant bioactive secondary metabolites [22]. In particular, hairy root (HR) technology has been reported to be an efficient system for producing secondary metabolites, especially for those which accumulate preferably in differentiated plant organs, such as roots [23]. A HR-based platform has been developed in our laboratory as a starting point to overcoming potential metabolic bottlenecks in the enzymatic reactions acting upstream or downstream of GGPP, and with the final aim to optimizing the biosynthesis of aethiopinone and other tricyclic abietane diterpenoids in _S. sclarea_, as summarized below. It is worthy to note that several bioactive diterpenes produced in the roots of other _Salvia_ species have been largely studied. For example, tanshinones, a class of lipophilic abietane diterpenes present in the roots of _S. miltiorrhyea_, known for their multiple therapeutic activities, have been deeply characterized, and their biosynthetic route from GGPP almost completely clarified [39]. Less is known on the enzymatic steps that from GGPP lead to the synthesis of abietane diterpenes synthesized in the roots of _S. sclarea_, which may hinder the possibility of genetically engineering genes encoding limiting enzymes with the final aim to increase the availability of substrates/intermediates/final products of this biosynthetic pathway.