Molecular insights on the biosynthesis of antitumour compounds by actinomycetes.
Bottom Line: The characterization of these clusters has represented, during the last 25 years, a great source of genes for the generation of novel derivatives by using combinatorial biosynthesis approaches: gene inactivation, gene expression, heterologous expression of the clusters or mutasynthesis.In addition, these techniques have been also applied to improve the production yields of natural and novel antitumour compounds.In this review we focus on some representative antitumour compounds produced by actinomycetes covering the genetic approaches used to isolate and validate their biosynthesis gene clusters, which finally led to generating novel derivatives and to improving the production yields.
Affiliation: Departamento de Biología Funcional and Instituto Universitario de Oncología del Principado de Asturias (I.U.O.P.A), Universidad de Oviedo, 33006 Oviedo, Spain.Show MeSH
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Mentions: The combination of targeting gene disruption and expression of genes or combinations of genes has been widely used to modify the glycosylation pattern of different antitumour compounds (Figs 6 and 7). The important antitumour drug 4′‐epidoxorubicin (epirubicin), traditionally obtained semisynthetically, along with its precursor 4′‐epidaunorubicin, was generated using a genetically engineered S. peucetius strain defective in the daunosamine biosynthesis gene dnmV. This strain was used to express the avermectin biosynthetic gene avrE from Streptomyces avermitilis or the erythromycin biosynthetic gene eryBIV from Saccharopolyspora erythraea, which led to 4′‐epianthracyclines (Madduri et al., 1998) (Fig. 6). A number of anthracyclines with modification in the glycosylation pattern have been obtained by expressing the steffimycin gene cluster in S. albus together with plasmids directing the biosynthesis of different deoxysugars. Three of these compounds showed higher antitumour activity than the parental natural product. In particular, d‐digitoxosyl‐8‐demethoxy‐10‐deoxysteffimycin (Fig. 7) was found to be 24‐fold more active than steffimycin when tested against different human tumour cell lines (Olano et al., 2008b). Analogues with improved activity of other aromatic compounds such as mithramycin and elloramycin have been also obtained by modification of the sugar moieties. The expression of genes involved in the biosynthesis of different deoxysugars in S. argillaceus led to 11 new mithramycin derivatives with altered glycosylation patterns (Baig et al., 2008; Pérez et al., 2008). Two of these, demycarosyl‐3D‐β‐d‐digitoxosyl‐mithramycin and deoliosyl‐3C‐β‐d‐mycarosyl‐mithramycin, showed improved activity against an oestrogen receptor‐positive human breast cancer cell line. In addition, demycarosyl‐3D‐β‐d‐digitoxosyl‐mithramycin was highly active against an oestrogen receptor‐negative human breast cancer cell line that is not strongly inhibited by mithramycin (Baig et al., 2008). On the other hand, coexpression of elloramycin gene cluster in S. albus with plasmids directing the biosynthesis of different deoxysugars has led to the isolation of new elloramycin (R1=CH3) and 8‐demethyl‐tetracenomycin C (R1=H) derivatives (Fig. 7) with different sugar moieties (Fischer et al., 2002; Rodríguez et al., 2002; Lombóet al., 2004b; Pérez et al., 2005; 2006). From these compounds, l‐mycarosyl‐elloramycin showed improved activity against three cancer cell lines (Lombóet al., 2004b). The modification of glycosylation patterns has not only been applied to polyketide natural products. Several indolocarbazole derivatives were generated by using this approach (Salas et al., 2005). Rebeccamycin, a DNA topoisomerase I inhibitor, and staurosporine, a promiscuous kinase inhibitor, contain a sugar moiety (Fig. 2) attached through a single N‐glycosidic bond (rebeccamycin) or by two N‐glycosidic bonds (staurosporine). The coexpression of rebeccamycin and staurosporine biosynthesis genes together with plasmids directing the biosynthesis of deoxysugars in S. albus has allowed the generation of novel derivatives from both compounds (Fig. 7). Some of these analogues were found highly active against specific kinases. l‐olivosyl‐arcyriaflavin A is a potent inhibitor of Ikkb, kinase that prevents activation of the NF‐κB pathway and thus has potential application on inflammation and cancer. On the other hand, l‐digitoxosyl‐k252c is a subnanomolar JAK2 inhibitor, kinase with potential application in myeloproliferative disorders (Sánchez et al., 2009).
Affiliation: Departamento de Biología Funcional and Instituto Universitario de Oncología del Principado de Asturias (I.U.O.P.A), Universidad de Oviedo, 33006 Oviedo, Spain.