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  • C12P19/44—Preparation of O-glycosides, e.g. glucosides
  • C12P19/56—Preparation of O-glycosides, e.g. glucosides having an oxygen atom of the saccharide radical directly bound to a condensed ring system having three or more carbocyclic rings, e.g. daunomycin, adriamycin

Definitions

• This invention relates to the gene cluster for aclacinomycin biosynthesis derived from Streptomyces galilaeus, and the use of the genes included therein to obtain hybrid antibiotics, or to increase yields of aclacinomycins or related antibiotics
• Anthracyclines are widely used anticancer agents Seven different anthracyclines are in worldwide clinical use daunorubicin, doxorubicin, ldarubicin, epirubicin, pirarubicin, zorubicin and aclarubicin A representative compound is doxorubicin, being the most efficient and acting on a wide array of malignancies A variety of toxic effects, like cumulative cardiotoxicity found with doxorubicin has sometimes led to discontinuation of the treatment Furthermore, there are some type of malignancies which do not respond to available anthracyclines The mechanism of action of anthracyclines, reflecting to their clinical efficiencies, is not clear, although most researchers consider inhibition of topo- isomerase II as a desired effect Generation of free radicals derived from quinonic structures is suggested to be related to side effects such as cardiotoxicity Anthracyclines have recently been reviewed by Professor Strohl and his group (1997)
• Aclacinomycin A (aclarubicin) first described by Oki et al (1975) is an anthracycline anti- biotic produced by Streptomyces galilaeus ATCC 31133 and S galilaeus ATCC 31615 It is active against tumor cells and exhibits alleviated toxic properties as compared with doxorubicin However, its activity does not reach solid tumors, limiting its use in leukemia treatment
• Aclarubicin differs from the other counterparts in its structure A trisaccha ⁇ de moiety, rhodosam ⁇ ne-2-deoxyfucose-c ⁇ nerulose A is attached at C-7 by a glycosidic bond, whereas at the corresponding position of daunomycins only one sugar residue, daunos- amme, is attached Despite the long history of anthracyclines, three decades or so, the studies on their biosynthesis are still going on, and there is further interest to obtain novel molecules for the development of cancer chemotherapeutics A method currently
• S galilaeus has been used as the host to prepare hybrid anthracyclines using the genes derived from rhodomycin pathway from S purpurascens (Niemi et al , 1994) and from nogalamycin biosynthesis cluster from S nogalater (Yhhonko et al , 1996a)
• the genes for nogalamycin pathway were used to generate the hybrid anthracychne production in S steffisburgensis producing typically steffimycin (Kunna ⁇ et al , 1997)
• biosynthesis genes for actinorhodin have been expressed in S galilaeus, resulting in the formation of aloesaponarin (Strohl et al , 1991)
• These hybrid compounds were modified in the aglycone moiety
• the biosynthesis genes involved in deoxyhexose pathway of nogalamycin were used to generate hybrid compounds using the S galilaeus mutants as hosts (FI pat appl
• the present invention concerns a gene cluster, most of the genes of which are derived from deoxyhexose pathway for rhodosamine, 2-deoxyfucose and/or rhodmose
• the gene cluster was cloned from S galilaeus ATCC 31615 and it is involved in biosynthesis of aclacino- mycins
• the present invention concerns particularly the discovery of the gene cluster for aclacino- mycin biosynthesis
• the cluster when introduced into S peucetius strains caused the production of hybrid antibiotics modified in their sugar moiety
• the probe for hybridization may be any known fragment that shows sufficient homology to the bio- synthetic cluster for aclarubicin sugars, to be able to hybridize with said cluster A DNA fragment which is identical to the desired region is preferred
• Sg- dht was obtained by PCR amplification of S galilaeus chromosomal DNA, using degenerated oligonucleotides annealing to the conserved region of 4,6-dehydratase gene
• 4,6- dehydratase is the first enzyme participating to a reaction series that converts a glucose molecule bound to a nucleotide into 6-deoxy sugars generally found in antibiotics
• this probe it was possible to clone the cluster of deoxyhexose pathway from a restricted gene library
• the library was prepared in a pUC-based plasmi
• the fragments, Sg4 and Sg5 were subcloned for sequencing in E. coh vectors pUC19 and pBluescript In total 30 subclones were used to obtain the nucleotide sequence of Sg4 and Sg5
• the sequenced cluster revealed thirteen genes involved in biosynthesis of aclacino- mycins Comparison with the sequences found in the sequence library suggested the functions as sga.2 for an activator, sga3 for a dehydratase, sga4 for oxidoreductase, sga5 for dTDP-glucose 4,6-dehydratase, sga6 for glycosyl transferase (GTF), sgal for a putative isomerase, sgaS for aklaviketone reductase, sga9 for a putative polyketide assembler, sgalO for a putative cyclase, sgal 1 for aminomethylase, sg
• Sg4 derived from pSgc4 was cloned in the Streptomyces expression vector pIJE486 (Ylihonko et al , 1996b) in S hvidans TK24 to give pSgs4
• This vector is a high copy number plasmid that replicates in several Streptomyces spp (Ward et al , 1986) and it contains a constitutively expressed promoter, ermE (Bibb et al , 1985) upstream from the multiple cloning site
• the plasmid pSgs4 isolated from TK24 was introduced into the S galilaeus strains that are blocked in deoxyhexose pathway of aclacinomycin biosynthesis and into the S peucetius mutants producing ⁇ -rhodomycinone based on a lesion in glycosylation genes The ability of aclacinomycin production was restored by three S galilaeus mutants, H063, H054
• FIG. 1 shows the structures of aclacinomycin, daunomycin and ⁇ -rhodomycinone
• FIG. 2 is a diagram of the gene cluster for aclacinomycin biosynthesis
• FIG. 3 describes the proposed biosynthesis pathway for sugars found in aclacinomycins
• FIG. 4 shows the structures of the hybrid compounds produced by M18/pSgs4 (1 and 2) and M90/pSgs4 (2)
• Restriction enzymes used were purchased from Promega (Mad ⁇ son,W ⁇ scons ⁇ n, USA), Fermentas (Lithuania) or Boehringer Mannheim (Germany), alkaline phosphatase from Boehringer Mannheim, and used according to manufacturers' instructions
• Proteinase K was purchased from Promega and lysozyme from Sigma HybondTM-N nylon membranes used in hybridization were purchased from Amersham (Buckinghamshire, England), DIG DNA Labelling Kit and DIG Luminescent Detection Kit from Boehringer Mannheim Qiaquick Gel Extraction Kit from Qiagen (Hilden, Germany) was used for isolating DNA from agarose
• Escherichia coh XLlBlueMRF' (Stratagene, La Jolla, California) was used for cloning
• Streptomyces lividans TK24 was the first cloning host for gene expression The strain was provided by prof Sir David Hopwood, John Innes Centre, UK The wild type, Streptomyces galilaeus ATCC 31615, produces aclacinomycins It was used here to donate the genes of the invention
• Streptomyces galilaeus H039 (Ylihonko et al, 1994) produces Akv-(Rho) 0 _ 3 It was used as an expression host for pSgs4 being more easily transformed than the other mutants or the wild type
• Streptomyces galilaeus H054 (Ylihonko et al, 1994) produces Akv-Rho-dF-(CinA) 0 _ ⁇ , Akv-dF-dF-(CinA) 0 . 1 and Akv-dF-Rho-Rho It was used as an expression host for pSgs4
• Streptomyces galilaeus H063 produces aklavinone It is a mutant strain derived from the wild type S. galilaeus H063 was used as an expression host for pSgs4
• Streptomyces galilaeus H065 produces aklavinone with neutral glycosides It is a mutant strain derived from the wild type S. galilaeus H065 was used as an expression host for pSgs4
• Streptomyces peucetius Ml 8 and M90 producing ⁇ -rhodomycinone are the mutants derived from S. peucetius var caesius (ATCC 27952) They were used as expression hosts for pSgs4
• E. coh cloning vectors pBluescript SK (Stratagene) and pUC19 (Pharmacia, Sweden) were used for making the subclones for sequencing and pBluescript was used also as a vector of a gene library
• pWHMl 109 (provided by prof CR Hutchinson, Wisconsin, USA) is a shuttle vector replicating in E. coh and in streptomycetes. It was used as a vector of a gene library
• pIJ486 is a high copy plasmid vector provided by prof. Sir David Hopwood, John Innes Centre, UK (Ward et al, 1986)
• pIJE486 (Ylihonko et al , 1996b) is an expression vector containing ermE (Bibb et al , 1985) to promote expression of the cloned genes
• Lysozyme solution (0 3 M sucrose, 25 mM Tris, pH 8 and 25mM EDTA, pH 8) was used to isolate total DNA TE buffer (10 mM Tris, pH 8 0 and ImM EDTA) was used to dissolve DNA
• the anthracychne metabolites were determined by (l) HPLC (LaChrom, Merck Hitachi, pump L-7100, detector L-7400 and integrator D-7500) using a LiChroCART RP-18 column Acetomtrile potassium hydrogen phosphate buffer (60 mM, pH 3 0 adjusted with citric acid) was used as a mobile phase Gradient system starting from 65 % to 30 % of potassium dihydrogen phosphate buffer was used to separate the compounds The flow rate was 1 ml/min and the detection was carried out at 480 nm, and (ii) by TLC using precoated Kieselgel 60 F 254 glass plates (Merck, Darmstadt, Germany) with an elution solution of toluene ethyl acetate methanol formic acid (50 50 15 3)
• ISP4 plates supplemented with thiostrepton 50 ⁇ g/ml were used to maintain the plasmid carrying cultures
• Streptomyces galilaeus was grown for four days in 50 ml of TSB medium supplemented with 0 5% glycine The cells were harvested by centrifuging for 15 min (3900 x g) in 12 ml Falcon tubes, and stored at -20 °C Cells from a 50 ml culture were used to isolate DNA 5 ml of lysozyme solution containing 5 mg/ml of lysozyme was added on the cells of each Falcon tube, and incubated for 20 min at 37°C 500 ⁇ l of 10% SDS contaimng 0 7 mg of proteinase K was added on the cells, and incubated for 80 min at 62 °C, another 500 ⁇ l of 10% SDS containing 0 7 mg of proteinase K was added, and incubation was continued for 60 min The sample was chilled on ice and 600 ⁇ l of 3M NaAc, pH 5 8 was added, and the mixture was extracted with equilibrated phenol (S
• Southern hybridization to determine suitable restriction enzymes for preparing the restricted plasmid libraries was carried out using BgHl, Xhol, Noil and their combinations A fragment of about 9 kb hybridizing with the Sg-dht probe was preferred For hybridization 600 ng of digested S.
• the probe for hybridization Sg-dht, which was used for colony hybridization as well, was obtained by amplifying a gene fragment from the S galilaeus DNA which is internal to the 4,6-dehydratase gene and corresponds to the fragment of 6345 to 6861 shown in SEQ ID NO 14 PCR was used for amplification, and the sequences for the degenerated o gonucleotide primers were 5 -CSGGSGSSGCS- GGSTTCATSGG-3' (forward, SEQ ID NO 15) and 5'-GGGWRCTGGYRSGGSCCG- TAGTTG-3' (reverse, SEQ ID NO 16) Suitable fragments were a 9 kb BgHl fragment
• the ligated DNA was introduced into E coh XLlBlueMRF' by electroporation Using the whole gation mixture 786 colonies were obtained The colonies were grown on agar plates for at least 12 h and transferred to nylon membranes Hybridization of colony membranes was carried out as Southern using Sg-dht as a probe Six clones gave signal in hybridization and the corresponding colonies were plated on agar and inoculated in 3 ml of LB medium for isolation of the plasmid DNA Southern hybridization was used to study whether the plasmids derived from the clones carried the desired insert Four of these plasmids contained the 4,6-dehydratase gene fragment and gave the identical restriction map thus carrying the same fragment representing both o ⁇ entations The fragment was designated as Sg4 and the plasmid containing the fragment as pSgc4
• E coh XLlBlueMRF' cells containing the subcloned plasmids were cultivated overnight at 37° C in 5 ml of LB-medium supplemented with 50 ⁇ g/ml of ampicil n
• Wizard Plus Mimpreps DNA Purification System kit of Promega or Biometra Silica Spin Disc Plasmid DNA Mimprep kit of Biomedizimsche Analytik Gmbh were used according to the manufacturers' instructions
• DNA sequencing was performed using the automatic ABI DNA sequencer (Perkin-Elmer) according to the manufacturer's instructions
• rhodinose that is enzymatically converted to cinerulose Aclacinomycin N, a precursor of aclarubicin, contains rhodinose as the third sugar residue
• Plasmid pSgs4 was introduced into S. lividans TK24 by protoplast transformation
• the strain S. lividans TK24/pSgs4 obtained was deposited according to the rules of the Budapest Treaty at Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ) on August 12, 1999 with the accession number DSM 12998
• the plasmid pSgs4 was isolated from the strain, and further transferred into S.
• M18/pSgs4 produced two compounds differing from the parental strain According to the HPLC and TLC data one compound was the same as was produced by M90/pSgs4, L- rhamnosyl- ⁇ -rhodomycinone, and the other one was L-daunosaminyl- ⁇ -rhodomycinone, which was previously characterized by Essery and Doyle (1980)
• H063 was completely complemented by pSgs4, the production level of aminogly- cosides was studied
• H063/pSgs4, H063 and the wild type S. galilaeus were cultivated in El medium in the Erlenmeyer bottles for four days
• Two samples of 2 ml from each culture were extracted first with toluene methanol (1 1) in acidic conditions to remove the neutral glycosides and the aglycones
• the extraction procedure was repeated until neutral glycosides and the aglycones had disappeared from the water phase
• the amount of anthracychne metabolites in toluene phase was determined and is shown in Table 3
• Aclacinomycins containing rhodosamine were extracted from the water phase by chloroform
• Both toluene and chloroform extracts were analyzed by TLC and toluene phases contained mostly aklavinone and the degradative products
• Chloroform phases contained mainly aminoglycosides,
• the seed culture 180 ml of El culture of the plasmid containing strains, M18/pSgs4 or M90/pSgs4, was obtained by cultivating each of the strains in three 250 ml Erlenmeyer flasks containing 50 ml of El-medium supplemented with thiostrepton (5 ⁇ g/ml) for four days at 30°C, 330 rpm.
• the combined culture broths (180 ml) were used to inoculate 13 1 of El -medium in a fermentor (Biostat E) Fermentation was carried out for five days at 28°C (330 rpm, aeration: 450 1/min).
• the cells were harvested by centrifuging. 2.6 1 of methanol was used to brake the bacterial cells.
• the anthracychne metabolites were extracted from methanol solution at pH 8 using 2 1 of ethyl acetate and the extract was evaporated to dryness. The viscous residue was loaded onto a silica column of 4 * 10 cm and toluene:ethyl acetate: formic acid (50:50:3) with increasing amount of methanol was used as an eluent. Pure fractions were pooled and extracted with 1M phosphate buffer (pH 8.0) and water. Organic phase was dried with anhydrous Na 2 SO 4 and then treated with hexane to effect precipitation. Pure compounds appeared as red powders dried under vacuum. Complete structural determination of the compounds were accomplished by NMR Proton and carbon assignments were based on a conventional NOE difference, pHSQC and HMBC measurements. Connectivities in particular relied heavily on HMBC experiment

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