Search

FK228 is an FDA-approved anticancer drug naturally produced by Chromobacterium violaceum No. 968 up to 19 mg/L in a pilot industry-scale batch fermentation. Here we report a genomics-guided discovery of Burkholderia thailandensis MSMB43 as a new and significantly better source of FK228. The genome of B. thailandensis MSMB43 was found to contain a functional biosynthetic gene cluster highly homologous to that of FK228 in C. violaceum No. 968, and the bacterium indeed produces authentic FK228. By simple fermentation in shaking flasks in a preferred M8 medium, B. thailandensis MSMB43 produced FK228 up to 67.7 mg/L; by fed-batch fermentation in a 20-L fermentor in M8 medium, B. thailandensis MSMB43 produced FK228 up to 115.9 mg/L, which is 95 fold higher than that of C. violaceum No. 968 under the same laboratory fermentation conditions. RT-PCR analysis indicated that the high FK228 yield of B. thailandensis MSMB43 was due to high expression of biosynthetic genes, represented by Bth_depA , during the fermentation process. Further genetic manipulation resulted in a recombinant strain, B. thailandensis MSMB43/pBMTL3- tdpR , which harbors a broad host-range vector expressing the thailandepsin biosynthetic pathway regulatory gene tdpR . This engineered strain produced up to 168.5 mg/L of FK228 in fed-batch fermentation in a 20-L fermentor in M8 medium. Therefore, the wild-type B. thailandensis MSMB43 or its engineered derivative could potentially be a good starting point for an industrial process to improve FK228 production for its expanding use in therapy.

Histone deacetylase (HDAC) inhibitors have emerged as a new class of anticancer drugs, with one synthetic compound, SAHA (vorinostat, Zolinza; 1), and one natural product, FK228 (depsipeptide, romidepsin, Istodax; 2), approved by FDA for clinical use. Our studies of FK228 biosynthesis in Chromobacterium violaceum no. 968 led to the identification of a cryptic biosynthetic gene cluster in the genome of Burkholderia thailandensis E264. Genome mining and genetic manipulation of this gene cluster further led to the discovery of two new products, thailandepsin A (6) and thailandepsin B (7). HDAC inhibition assays showed that thailandepsins have selective inhibition profiles different from that of FK228, with comparable inhibitory activities to those of FK228 toward human HDAC1, HDAC2, HDAC3, HDAC6, HDAC7, and HDAC9 but weaker inhibitory activities than FK228 toward HDAC4 and HDAC8, the latter of which could be beneficial. NCI-60 anticancer screening assays showed that thailandepsins possess broad-spectrum antiproliferative activities with GI50 for over 90% of the tested cell lines at low nanomolar concentrations and potent cytotoxic activities toward certain types of cell lines, particularly for those derived from colon, melanoma, ovarian, and renal cancers. Thailandepsins thus represent new naturally produced HDAC inhibitors that are promising for anticancer drug development.